Small cell antennas suitable for mimo operation

ABSTRACT

A base station antenna includes a first set of radiating elements that are configured to generate a first antenna beam that has a first peanut-shaped antenna pattern in an azimuth plane and a second set of radiating elements that are configured to generate a second antenna beam that has a second peanut-shaped antenna pattern in the azimuth plane. A longitudinal axis of the first peanut-shaped antenna pattern in the azimuth plane is rotated approximately ninety degrees from a longitudinal axis of the second peanut-shaped antenna pattern in the azimuth plane.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 to U.S.Provisional Patent Application Ser. No. 62/533,762, filed Jul. 18, 2017,the entire content of which is incorporated herein by reference as ifset forth in its entirety.

FIELD

The present invention relates to cellular communications systems and,more particularly, to base station antenna for small cell cellular basestations.

BACKGROUND

Cellular communications systems are well known in the art. In a typicalcellular communications system, a geographic area is divided into aseries of regions that are referred to as “cells,” and each cell isserved by a base station. Typically, a cell may serve users who arewithin a distance of, for example, 2-20 kilometers from the basestation, although smaller cells are typically used in urban areas toincrease capacity. The base station may include baseband equipment,radios and antennas that are configured to provide two-way radiofrequency (“RF”) communications with mobile subscribers that arepositioned throughout the cell. In many cases, the cell may be dividedinto a plurality of “sectors,” and separate antennas provide coverage toeach of the sectors. The antennas are often mounted on a tower or otherraised structure, with the radiation beam (“antenna beam”) that isgenerated by each antenna directed outwardly to serve a respectivesector. Typically, a base station antenna includes one or morephase-controlled arrays of radiating elements, with the radiatingelements arranged in one or more vertical columns when the antenna ismounted for use. Herein, “vertical” refers to a direction that isperpendicular relative to the plane defined by the horizon.

In order to increase capacity, cellular operators have, in recent years,been deploying so-called “small cell” cellular base stations. A smallcell base station refers to a low-power base station that may operate inthe licensed and/or unlicensed spectrum that has a much smaller rangethan a typical “macrocell” base station. A small cell base station maybe designed to serve users who are within short distances from the smallcell base station (e.g., tens or hundreds of meters). Small cells may beused, for example, to provide cellular coverage to high traffic areaswithin a macrocell, which allows the macrocell base station to offloadmuch or all of the traffic in the vicinity of the small cell to thesmall cell base station. Small cells may be particularly effective inLong Term Evolution (“LTE”) cellular networks in efficiently using theavailable frequency spectrum to maximize network capacity at areasonable cost. Small cell base stations typically employ an antennathat provides full 360 degree coverage in the azimuth plane and asuitable beamwidth in the elevation plane to cover the designed area ofthe small cell. In many cases, the small cell antenna will be designedto have a small downtilt in the elevation plane to reduce spill-over ofthe antenna beam of the small cell antenna into regions that are outsidethe small cell and also for reducing interference between the small celland the overlaid macro cell.

SUMMARY

Pursuant to embodiments of the present invention, base station antennasare provided that include first through eighth linear arrays ofradiating elements that are mounted to extend outwardly from respectivefirst through eighth backplanes. A first feed network is coupled to thefirst and third linear arrays of radiating elements, a second feednetwork is coupled to the second and fourth linear arrays of radiatingelements, a third feed network hat is coupled to the fifth and seventhlinear arrays of radiating elements, and a fourth feed network iscoupled to the sixth and eighth linear arrays of radiating elements. Thefirst linear array of radiating elements is positioned generallyopposite the third linear array of radiating elements, the second lineararray of radiating elements is positioned generally opposite the fourthlinear array of radiating elements, the fifth linear array of radiatingelements is positioned generally opposite the seventh linear array ofradiating elements, and the sixth linear array of radiating elements ispositioned generally opposite the eighth linear array of radiatingelements.

In some embodiments, the first through eighth backplanes may togetherdefine a tube. The tube may have, for example, a generally octagonaltransverse cross-section.

In some embodiments, the first and third linear arrays of radiatingelements may be configured to generate a first antenna beam that has apeanut-shaped cross-section in the azimuth plane, and the second andfourth linear arrays of radiating elements may be configured to generatea second antenna beam that has a peanut-shaped cross-section in theazimuth plane. Likewise, the fifth and seventh linear arrays ofradiating elements may be configured to generate a third antenna beamthat has a peanut-shaped cross-section in the azimuth plane, and thesixth and eighth linear arrays of radiating elements may be configuredto generate a fourth antenna beam that has a peanut-shaped cross-sectionin the azimuth plane.

In some embodiments, the first and third linear arrays of radiatingelements may be configured to generate a first antenna beam at a firstpolarization and a second antenna beam at a second polarization that isopposite the first polarization, and the second and fourth linear arraysof radiating elements are configured to generate a third antenna beam atthe first polarization and a fourth antenna beam at the secondpolarization. In such embodiments, the first and third linear arrays ofradiating elements may be configured to operate as atwo-input-two-output multi-input-multi-output (“MIMO”) antenna and thesecond and fourth linear arrays of radiating elements may be configuredto operate as a two-input-two-output MIMO antenna.

In some embodiments, the first through eight linear arrays of radiatingelements may be configured to transmit and receive RF signals in a firstfrequency band.

In some embodiments, the above-described base station antenna mayfurther include ninth through twelfth linear arrays of radiatingelements that are mounted to extend outwardly from respective ninththrough twelfth backplanes. These base station antennas may include afifth feed network that is coupled to the ninth and eleventh lineararrays of radiating elements and a sixth feed network that is coupled tothe tenth and twelfth linear arrays of radiating elements. The ninthlinear array of radiating elements may be positioned generally oppositethe eleventh linear array of radiating elements, and the tenth lineararray of radiating elements may be positioned generally opposite thetwelfth linear array of radiating elements. The first through twelfthbackplanes may together define a tube having a generally dodecagonaltransverse cross-section. The first through twelfth linear arrays ofradiating elements may be configured to transmit and receive RF signalsin a first frequency band.

Pursuant to further embodiments of the present invention, base stationantennas are provided that include at least first through eighth lineararrays of radiating elements that are radially mounted on a tubularreflector assembly as four opposed pairs of linear arrays of radiatingelements.

In some embodiments, these base station antennas may further includefirst through fourth ports, and the first and third linear arrays may becommonly fed via the first port, the second and fourth linear arrays maybe commonly fed via the second port, the fifth and seventh linear arraysmay be commonly fed via the third port, and the sixth and eighth lineararrays may be commonly fed via the fourth port.

In some embodiments, the tubular reflector assembly may have one of anoctagonal, a dodecagon or a hexadecagon cross-section in the azimuthplane.

In some embodiments, each opposed pair of linear arrays of radiatingelements may be configured to generate an antenna beam that has apeanut-shaped cross-section in the azimuth plane.

In some embodiments, each of the first through eighth linear arrays ofradiating elements may be mounted on a respective one of the firstthrough eighth backplanes of the tubular reflector assembly, and atleast some of the first through eighth backplanes may include arespective additional linear array of radiating elements that isconfigured to operate in a different RF band.

In some embodiments, each additional linear array of radiating elementsmay be collinear with a respective one of the first through eighthlinear arrays of radiating elements.

Pursuant to still further embodiments of the present invention, basestation antennas are provided that include a first set of radiatingelements that are configured to generate a first antenna beam thatcovers a first sector in an azimuth plane and a third sector in theazimuth plane, a second set of radiating elements that are configured togenerate a second antenna beam that covers a second sector in theazimuth plane and a fourth sector in the azimuth plane, a third set ofradiating elements that are configured to generate a third antenna beamthat covers a fifth sector in an azimuth plane and a seventh sector inthe azimuth plane and a fourth set of radiating elements that areconfigured to generate a fourth antenna beam that covers a sixth sectorin the azimuth plane and an eighth sector in the azimuth plane. Thesecond sector is between the first sector and the third sector, thefourth sector is between the first sector and the third sector andopposite the second sector, the sixth sector is between the fifth sectorand the seventh sector, and the eight sector is between the fifth sectorand the seventh sector and opposite the sixth sector.

In some embodiments, the first set of radiating elements may comprise afirst subset of radiating elements that are arranged as a first lineararray of radiating elements and a third subset of radiating elementsthat are arranged as a third linear array of radiating elements, wherethe third linear array of radiating elements is mounted opposite thefirst linear array of radiating elements. In some embodiments, thesecond set of radiating elements may comprise a second subset ofradiating elements that are arranged as a second linear array ofradiating elements and a fourth subset of radiating elements that arearranged as a fourth linear array of radiating elements, where thefourth linear array of radiating elements is mounted opposite the secondlinear array of radiating elements.

In some embodiments, the first linear array of radiating elements maypoint in a direction opposite a pointing direction of the third lineararray of radiating elements.

In some embodiments, the first through fourth sets of radiating elementsmay be mounted on a tubular reflector assembly that has an octagonal, adodecagon or a hexadecagon cross-section in the azimuth plane.

In some embodiments, the first through fourth antenna beams may eachhave a peanut-shaped cross-section in the azimuth plane.

In some embodiments, the first and second antenna beams may togetherprovide omnidirectional coverage in the azimuth plane, and where thethird and fourth antenna beams may together provide omnidirectionalcoverage in the azimuth plane.

In some embodiments, the base station antenna may further include afirst feed network that is coupled to the first and third linear arraysof radiating elements, a second feed network that is coupled to thesecond and fourth linear arrays of radiating elements, a third feednetwork that is coupled to the fifth and seventh linear arrays ofradiating elements, and a fourth feed network that is coupled to thesixth and eighth linear arrays of radiating elements.

In some embodiments, the first feed network may feed the first subset ofradiating elements out-of-phase with respect to third subset ofradiating elements.

Pursuant to additional embodiments of the present invention, basestation antennas are provided that include first through fourth sets ofradiating elements that are configured to generate respective firstthrough fourth antenna beams that have respective first through fourthpeanut-shaped cross-sections in the azimuth plane. A longitudinal axisof the first antenna beam in the azimuth plane is rotated approximatelyninety degrees from a longitudinal axis of the second antenna beam inthe azimuth plane and a longitudinal axis of the third antenna beam inthe azimuth plane is rotated approximately ninety degrees from alongitudinal axis of the fourth antenna beam in the azimuth plane, andthe longitudinal axis of the third antenna beam in the azimuth plane isrotated approximately forty-five degrees from a longitudinal axis of thefirst antenna beam in the azimuth plane.

In some embodiments, the first set of radiating elements may comprise afirst subset of radiating elements that are arranged as a first lineararray of radiating elements and a third subset of radiating elementsthat are arranged as a third linear array of radiating elements, and thesecond set of radiating elements may comprise a second subset ofradiating elements that are arranged as a second linear array ofradiating elements and a fourth subset of radiating elements that arearranged as a fourth linear array of radiating elements.

In some embodiments, the third linear array of radiating elements may bemounted opposite the first linear array of radiating elements and thefourth linear array of radiating elements may be mounted opposite thesecond linear array of radiating elements.

In some embodiments, the first through eighth linear arrays of radiatingelements may be mounted on respective first through eighth majorsurfaces of a tubular reflector assembly that may have an octagonal, adodecagon or a hexadecagon cross-section in the azimuth plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a highly simplified schematic diagram illustrating a smallcell cellular base station.

FIG. 1B illustrates an antenna beam that may be generated by the antennaof the small cell base station of FIG. 1A.

FIG. 2A is a schematic diagram illustrating a small cell base stationantenna that uses polarization diversity and horizontal spatialdiversity to implement 4× MIMO capabilities.

FIG. 2B is another schematic view of the small cell base station of FIG.2A.

FIGS. 2C and 2D are graphs illustrating azimuth and elevationcross-sections of the antenna beam of the small cell antenna of FIG. 2A.

FIGS. 3A and 3B are a side view and a top view, respectively, of two ofthe radiating elements included in the base station antenna of FIG. 2A.

FIG. 4 is a block diagram illustrating the feed networks that may beincluded in the base station antenna of FIG. 2A.

FIG. 5A is a schematic diagram illustrating another small cell basestation antenna that uses polarization diversity and vertical spatialdiversity to implement 4× MIMO capabilities.

FIGS. 5B and 5C are graphs illustrating the azimuth and elevationcross-sections of the antenna beam of the small cell antenna of FIG. 5A.

FIG. 6A is a schematic diagram illustrating a small cell base stationantenna according to embodiments of the present invention that formsantenna beams having peanut shaped cross-sections in the azimuth planeto provide small cell coverage with MIMO capabilities.

FIGS. 6B and 6C are graphs illustrating azimuth and elevationcross-sections of the antenna beams of the small cell antenna of FIG.6A.

FIG. 7 is a block diagram illustrating the feed networks that may beincluded in the base station antenna of FIG. 6A.

FIGS. 8 and 9 are graphs that compare the performance of the antenna ofFIG. 6A to the antennas of FIG. 2A and FIG. 5A, respectively

FIG. 10 is a schematic diagram illustrating a multi-band small cell basestation antenna according to further embodiments of the presentinvention.

FIG. 11 is a schematic diagram illustrating a modified version of themulti-band small cell base station of FIG. 10.

FIG. 12 is a schematic diagram illustrating a multi-band small cell basestation antenna according to still further embodiments of the presentinvention.

FIG. 13A is a schematic diagram illustrating a small cell base stationantenna according to embodiments of the present invention that forms asingle antenna beam that may provide coverage for more than 180 degreesin the azimuth plane to provide small cell coverage with MIMOcapabilities.

FIG. 13B is a graph illustrating the azimuth cross-section of an antennabeam that may be generated by the small cell antenna of FIG. 13A whenthe radiating elements thereof are fed in-phase.

FIG. 13C is a graph illustrating the azimuth cross-section of an antennabeam that may be generated by the small cell antenna of FIG. 13A whenthe radiating elements thereof are fed 180 degrees out-of-phase.

FIG. 13D is a graph illustrating the azimuth cross-section of an antennabeam that may be generated by the small cell antenna of FIG. 13A whenthe radiating elements thereof are fed 170 degrees out-of-phase.

FIG. 13E is a graph illustrating the azimuth cross-section of an antennabeam that may be generated by the small cell antenna of FIG. 13A whenthe radiating elements thereof are fed 90 degrees out-of-phase.

FIG. 14A is a schematic diagram illustrating a feed network that may beused to feed a pair of linear arrays of radiating elements out-of-phase.

FIG. 14B is a schematic diagram illustrating an alternative feed networkthat may be used to feed a pair of linear arrays of radiating elementsout-of-phase.

FIG. 15 is a schematic diagram illustrating a dual-band small cell basestation antenna according to embodiments of the present invention thatuses out-of-phase feeding techniques in each of the two frequency bandsof operation to enhance the coverage in the azimuth plane.

FIG. 16A is a schematic diagram illustrating a small cell base stationantenna according to still further embodiments of the present invention.

FIG. 16B is a block diagram illustrating how the low-band radiatingelements of the small cell base station antenna of FIG. 16A may beconnected to a four-port radio.

FIGS. 17A and 17B are schematic diagrams illustrating small cell basestation antennas according to additional embodiments of the presentinvention.

FIGS. 18 and 19 are schematic diagrams illustrating small cell basestation antennas according to yet additional embodiments of the presentinvention.

FIG. 20A is a schematic plan view illustrating the antenna beams formedby a small cell antenna according to embodiments of the presentinvention that includes a tubular reflector having a squarecross-section.

FIG. 20B is a schematic plan view illustrating the antenna beams formedby a small cell antenna according to embodiments of the presentinvention that includes a tubular reflector having an octagonalcross-section.

FIGS. 21A-21D are schematic diagrams illustrating a small cell basestation antennas according to embodiments of the present invention thatare formed on tubular reflectors that have octagonal cross-sections.

FIG. 21E is a schematic diagram illustrating how the linear arrays ofthe antenna of FIG. 21A can be fed in greater detail.

FIGS. 22A-22D are schematic plan views illustrating the antenna beamsformed by a small cell antenna according to embodiments of the presentinvention that include tubular reflectors having dodecagoncross-sections.

FIG. 23 is a schematic plan view illustrating the antenna beams formedby a small cell antenna according to embodiments of the presentinvention that includes a tubular reflector having a hexadecagoncross-section.

DETAILED DESCRIPTION

Pursuant to embodiments of the present invention, small cell antenna areprovided that support MIMO operation that may be simpler and lessexpensive than conventional small cell antennas. In some embodiments,the small cell antenna may include four linear arrays of radiatingelements that are mounted on the four main faces of a rectangulartubular reflector assembly. The first and third linear arrays may bemounted on opposed main faces of the rectangular tubular reflectorassembly and may be commonly fed to generate a first antenna beam thathas a peanut shaped cross-section in the azimuth plane. The second andfourth linear arrays may be mounted on the other two opposed main facesof the rectangular tubular reflector assembly and may be commonly fed togenerate a second antenna beam that also has a peanut shapedcross-section in the azimuth plane. The second antenna pattern may havethe same shape as the first antenna pattern and may be rotatedapproximately ninety degrees with respect to the first antenna patternin the azimuth plane. Together, the peanut-shaped first and secondantenna patterns may form a suitable omnidirectional antenna pattern inthe azimuth plane.

In some embodiments, the radiating elements in the first through fourthlinear arrays may comprise dual-polarized radiating elements such as,for example, slant −45°/+45° cross-dipole radiating elements. Whendual-polarized radiating elements are used, a first port on the radiomay be used to commonly feed radiators having a first polarization thatare included in the radiating elements of the first and third lineararrays, and a second port on the radio may be used to commonly feedradiators having a second polarization that are included in theradiating elements of the first and third linear arrays. Similarly, athird port on the radio may be used to commonly feed radiators havingthe first polarization that are included in the radiating elements ofthe second and fourth linear arrays, and a fourth port on the radio maybe used to commonly feed radiators having the second polarization thatare included in the radiating elements of the second and fourth lineararrays. The above-described small cell antenna may be used for 4× MIMOtransmissions.

In some embodiments, the small cell antennas may comprise single-bandantennas that have linear arrays of radiating elements that all operatein the same frequency bands (which may be a frequency band that supportsa single type of cellular service or a frequency band that encompassesmultiple types of cellular service). In other embodiments, multi-bandsmall cell antenna may be provided that include at least two sets oflinear arrays, where the linear arrays in the first set includeradiating elements that are configured to transmit and receive RFsignals in a first frequency band and the linear arrays in the secondset include radiating elements that are configured to transmit andreceive RF signals in a second frequency band that is different from thefirst frequency band.

In some embodiments, the linear arrays of the small cell base stationantennas may be fed in-phase, meaning that the phase of thesub-components of the RF signal that are provided to the radiatingelements of a first linear array is the same as the phase of thesub-components of the RF signal that are provided to the radiatingelements of a second linear array. In other embodiments, the feednetworks may be designed to feed at least some of the linear arraysout-of-phase such that the phase of the sub-components of the RF signalthat are provided to the radiating elements of a first linear array isdifferent than the phase of the sub-components of the RF signal that areprovided to the radiating elements of a second linear array.Out-of-phase feeding may provide improved performance (e.g., a broaderbi-directional pattern that may be closer in shape to an omnidirectionalpattern in the azimuth plane) in some circumstances, particularly withrespect to signals in lower frequency ranges. The out-of-phase feedingmay involve feeding the linear arrays with sub-components of an RFsignal that are about 180 degrees out-of-phase or with smaller phasedifferences. Out-of-phase feeding may, in some cases, reduce the maximumdirectivity of the antenna beam, but increase the area where the antennadirectivity exceeds a pre-determined level, thereby providing a patternthat has a somewhat omnidirectional shape with coverage gaps therein.Such patterns may be well-suited for small cell base stations that arewithin the coverage area of a macrocell base station.

Example embodiments of the invention will now be discussed in moredetail with reference to the attached drawings.

With the introduction of various fourth generation (“4G”) and fifthgeneration (“5G”) cellular technologies, base stations are employingantennas that have multi-input-multi-output (“MIMO”) capabilities. Asknown to those of skill in the art, MIMO refers to a technique where asignal is output through multiple ports of a radio and transmittedthrough multiple different antenna arrays (or sub-arrays) that are, forexample, spatially separated from one another and/or at orthogonalpolarizations. The amplitudes and phases of the signals transmittedthrough the different ports may be set so that the signals transmittedthrough the multiple antennas will constructively combine at the userdevice. The use of MIMO transmission techniques may help overcome thenegative effects of multipath fading, reflections of the transmittedsignal off of buildings and the like to provide enhanced transmissionquality and capacity.

Small cell base stations are often implemented in high-density urbanenvironments. These environments may have numerous buildings which makethese environments natural applications for using MIMO transmissiontechniques. MIMO is typically employed in 4G applications because, whilemore expensive, the added capacity typically justifies the increasedcost. If the costs of MIMO capable base station antennas can be reducedthen the benefits of using MIMO transmission techniques in terms ofnetwork capacity as a function of capital expense may be furtherincreased.

Referring to FIG. 1A, a small cell base station 10 is illustrated. Thebase station 10 includes an antenna 20 that may be mounted on a raisedstructure 30. In the depicted embodiment, the structure 30 is a smallantenna tower, but it will be appreciated that a wide variety ofmounting locations may be used including, for example, utility poles,buildings, water towers and the like. The antenna 20 may have anomnidirectional antenna pattern in the azimuth plane, meaning that theantenna beam generated by the antenna 20 may extend through a full 360degree circle in the azimuth plane, and may have a suitable beamwidth(e.g., 10-30 degrees) in the elevation plane. The antenna beam may beslightly down-tilted in the elevation plane to reduce interference withadjacent base stations.

The small cell base station 10 further includes base station equipmentsuch as baseband units 40 and radios 42. A single baseband unit 40 and asingle radio 42 are shown in FIG. 1A to simplify the drawing, but itwill be appreciated that more than one baseband unit 40 and/or radio 42may be provided. Additionally, while the radio 42 is shown as beingco-located with the baseband equipment 40 at the bottom of the antennatower 30, it will be appreciated that in other cases the radio 42 may bea remote radio head that is mounted on the antenna tower 30 adjacent theantenna 20. As is known to those of skill in the art, the baseband unit40 may receive data from another source such as, for example, a backhaulnetwork (not shown) and may process this data and provide a data streamto the radio 42. The radio 42 may generate RF signals that include thedata encoded therein and may amplify and deliver these RF signals to theantenna 20 for transmission via a cabling connection 44. It will also beappreciated that the base station 10 of FIG. 1A will typically includevarious other equipment (not shown) such as, for example, a powersupply, back-up batteries, a power bus, Antenna Interface Signal Group(“AISG”) controllers and the like.

FIG. 1B is a composite of several views of an antenna beam 60 having anomnidirectional pattern in the azimuth plane that may be generated bythe antenna 20. In particular, FIG. 1B includes a perspectivethree-dimensional view of the antenna beam 60 (labelled “3D pattern”) aswell as plots of the azimuth and elevation patterns thereof. The azimuthpattern is generated by taking a horizontal cross-section through themiddle of the three dimensional antenna beam 60, and the elevationpattern is generated by taking a vertical cross-section through themiddle of the three dimensional beam 60. The three-dimensional patternin FIG. 1B illustrates the general shape of the generated antenna beamin three dimensions. As can be seen, the antenna beam 60 extends througha full 360 degrees in the azimuth plane, and the antenna beam 60 mayhave a nearly constant gain in all directions in the azimuth plane. Inthe elevation plane, the antenna beam 60 has a high gain in the azimuthplane (i.e., parallel to the horizon), but the gain drops offdramatically both above and below the horizon. The antenna beam 60 thusis omnidirectional in the azimuth plane and directional in the elevationplane.

FIG. 2A is a schematic diagram illustrating a small cell base stationantenna 100 that may be used to implement the antenna 20 of FIG. 1A. Thesmall cell base station antenna 100 is configured to use polarizationand horizontal spatial diversity to provide 4× MIMO capabilities. 4×MIMO refers to an antenna that can transmit a MIMO signal along fourdifferent paths (e.g., through four spatially separated arrays orthrough two spatially separated arrays that each transmit signals at twodifferent orthogonal polarizations).

As shown in FIG. 2A, the small cell base station antenna 100 includes atubular triangular reflector assembly 110. The base station antenna 100further includes six linear arrays 120-1 through 120-6 of radiatingelements 122. Each face of the triangular reflector assembly 110 maycomprise a backplane 112-1, 112-2, 112-3. Each backplane 112 maycomprise a unitary structure or may comprise a plurality of structuresthat are attached together. Each backplane 112 may comprise, forexample, a reflector that serves as a ground plane for the radiatingelements 122 of the linear arrays 120 mounted thereon. In someembodiments, the backplanes 112-1, 112-2, 112-3 may comprise a unitaryor monolithic structure that serves as all three backplanes 112-1,112-2, 112-3. It should be noted that herein when multiple like orsimilar elements are provided they may be labelled in the drawings usinga two part reference numeral (e.g., backplane 112-2). Such elements maybe referred to herein individually by their full reference numeral(e.g., backplane 112-2) and may be referred to collectively by the firstpart of their reference numeral (e.g., the backplanes 112).

Two linear arrays 120 are mounted on each backplane 112. Each lineararray 120 is mounted to be oriented vertically with respect to thehorizon when the base station antenna 100 is mounted for use. In thedepicted embodiment, each linear array 120 includes a total of sixradiating elements 122. It will be appreciated, however, that anyappropriate number of radiating elements 122 may be included in thelinear arrays 120. Each of the radiating elements 122 may be identical.The radiating elements 122 may extend forwardly from the respectivebackplanes 112 (see FIG. 2B).

In an example embodiment, each linear array 120 may be implemented asthree sub-arrays 121 of radiating elements 122, where each sub-array 121includes two radiating elements 122 that are mounted on a commonfeedboard. An example and non-limiting implementation of such asub-array 121 is depicted in FIGS. 3A-3B. It will be appreciated,however, that sub-arrays 121 may or may not be used in otherembodiments, and that any appropriate radiating elements 122 may beused. It will also be appreciated that different types of radiatingelements 122 may be more suitable for different frequency bands ofoperation.

Referring now to FIGS. 3A and 3B, it can be seen that each sub-array 121may comprise a pair of radiating elements 122 that are mounted on acommon feedboard 128. Each radiating element 122 may comprise a pair ofstalks 124-1, 124-2 and a pair of radiators 126-1, 126-2. Each stalk 124may comprise a microstrip printed circuit board. The two printed circuitboards that form the stalks 124-1, 124-2 may be arranged in an “X”configuration when viewed from above. Each radiator 126 may comprise,for example, a dipole. In the depicted embodiment, the base stationantenna 100 is a dual-polarized antenna, and hence each radiatingelement 122 includes a pair of dipole radiators 126 arranged in aso-called “cross-dipole” arrangement. Each radiator (dipole) 126 may bedisposed in a plane that is substantially perpendicular to alongitudinal axis of its corresponding stalk 124. In the depictedembodiment, each sub-array 121 includes a pair of radiating elements 122that are mounted on a feedboard 128. The feedboard 128 may be configuredto split an RF signal that is provided thereto into two sub-componentsand to feed each sub-component to a respective one of the radiatingelements 122. Directors 127 may be mounted above the radiators 126 tonarrow the beamwidth of the radiating elements 122.

It will be appreciated that the base station antenna 100 may include anumber of conventional components that are not depicted in FIG. 2A. Forexample, the base station antenna 100 may include a radome 160 thatcovers and protects the radiating elements 122 and other components ofthe base station antenna 100. The radome 160 may be formed of, forexample, extruded plastic. The radome may 160 may be substantiallytransparent to RF energy in the frequency range in which the basestation antenna 100 is designed to operate. FIG. 2B is another schematicview of the base station antenna 100 that schematically depicts such aradome 160. The base station antenna 100 may further include a pluralityof RF connectors that allow respective radios (not shown) of the basestation to be connected to base station antenna 100. The base stationantenna 100 may also include additional connectors in some embodimentssuch as, for example, AISG connectors that are used to transmit controlsignals to the base station antenna to, for example, control anelectronic down-tilt of the linear arrays 120.

A plurality of circuit elements and other structures may be mountedwithin the reflector assembly 110. These circuit elements and otherstructures may include, for example, phase shifters for one or more ofthe linear arrays 120, remote electronic tilt (RET) actuators formechanically adjusting the phase shifters, one or more controllers,cabling connections, RF transmission lines and the like. Mountingbrackets (not shown) may also be provided for mounting the base stationantenna 100 to another structure such as an antenna tower or utilitypole.

FIG. 4 illustrates an embodiment of four feed networks 150-1 through150-4 that may be used to pass RF signals between the base station radio42 and the radiating elements 122 of the linear arrays 120. As shown inFIG. 4, the radio 42 is a four port device having ports 44-1 through44-4. Duplexing of the transmit and receive channels is performedinternal to the radio 42, so each port 44 on the radio 42 passes bothtransmitted and received RF signals. The provision of four ports 44 onradio 42 allows the radio 42 to feed signals to different subsets of thelinear arrays 120 of base station antenna 100 at two different(orthogonal) polarizations. Since the base station antenna 100 has slant−45°/+45° cross-dipole radiating elements 122, herein the twopolarizations will be referred to as the −45° and the +45°polarizations. It will be appreciated, however, that any suitable typesof orthogonal polarizations may be used (e.g., horizontal/vertical,right hand circular/left hand circular, etc.). Four connectors 152 maybe provided on base station antenna 100 and cables 46 (e.g., coaxialcables) may connect each port 44 on the radio 42 to a respective one ofthese RF connectors 152.

As shown in FIG. 4, the first port 44-1 of radio 42 is coupled to theradiators 126 of the radiating elements 122 of linear arrays 120-1,120-3, 120-5 that are arranged to transmit/receive signals having a −45°polarization via a first 1×3 power splitter/combiner 170-1. An RFtransmission line (e.g., a coaxial cable) may extend between theconnector 152 and the splitter/combiner 170-1. The 1×3 splitter/combiner170-1 may split RF signals received from port 44-1 into three equalpower sub-components. Each output of the splitter 170-1 may be fed to arespective phase shifter 180-1, 180-3, 180-5 that is associated with arespective linear array 120-1, 120-3, 120-5.

The second port 44-2 of radio 42 is coupled to the radiators 126 of theradiating elements 122 of linear arrays 120-1, 120-3, 120-5 that arearranged to transmit/receive signals having a +45° polarization via asecond 1×3 power splitter/combiner 170-2. The 1×3 splitter/combiner170-2 may split RF signals received from port 44-2 into three equalpower sub-components that are fed to respective phase shifters 182-1,182-3, 182-5 that are associated with the respective linear arrays120-1, 120-3, 120-5. Similarly, the third port 44-3 of radio 42 iscoupled to the radiators 126 of the radiating elements 122 of lineararrays 120-2, 120-4, 120-6 that are arranged to transmit/receive signalshaving a −45° polarization via a third 1×3 power splitter/combiner 170-3which splits RF signals received from port 44-3 into three equal powersub-components that are fed to respective phase shifters 180-2, 180-4,180-6 that are associated with the respective linear arrays 120-2,120-4, 120-6. The fourth port 44-4 of radio 42 is coupled to theradiators 126 of the radiating elements 122 of linear arrays 120-2,120-4, 120-6 that are arranged to transmit/receive signals having a +45°polarization via a fourth 1×3 power splitter/combiner 170-4 which splitsRF signals received from port 44-4 into three equal power sub-componentsthat are fed to respective phase shifters 182-2, 182-4, 182-6 that areassociated with the respective linear arrays 120-2, 120-4, 120-6.

As shown in FIG. 4, each phase shifter 180, 182 may split the RF signalsinput thereto three ways (and the power split may be equal or unequal)and may apply a phase taper across the three sub-components of the splitRF signal to, for example, apply an electronic downtilt to the antennabeam that is formed when the sub-components of the RF signal aretransmitted (or received) through the respective linear arrays 120 ofradiating elements 122. Each of the three outputs of each phase shifter180, 182 may be connected to a respective one of three feedboards 128that are included in each linear array 120. As noted above, eachfeedboard 128 receives a respective sub-component of the RF signal,splits it into two parts, and feeds each part to a radiator 126 of arespective one of the radiating elements 122 mounted on the feedboard128. In this fashion, the radio 42 may be used to transmit an RF signalvia MIMO transmission techniques through four different paths throughbase station antenna 100, namely a first path using the −45° radiators126 of the radiating elements 122 of linear arrays 120-1, 120-3, 120-5,a second path using the +45° radiators 126 of the radiating elements 122of linear arrays 120-1, 120-3, 120-5, a third path using the −45°radiators 126 of the radiating elements 122 of linear arrays 120-2,120-4, 120-6 and a fourth path using the +45° radiators 126 of theradiating elements 122 of linear arrays 120-2, 120-4, 120-6.

Thus, as explained above, the base station antenna 100 may implement 4×MIMO by transmitting an RF signal at two different polarizations throughtwo different sets of three linear arrays (namely linear arrays 120-1,120-3, 120-5 and linear arrays 120-2, 120-4, 120-6). FIGS. 2C and 2D aregraphs illustrating the antenna beam generated by base station antenna100 in the azimuth and elevation planes, respectively. As shown in FIGS.2C and 2D, the antenna beam has an omnidirectional shape in the azimuthplane and has a relatively narrow elevation beamwidth. The linear arrays120 on each backplane 112 may be spaced apart horizontally by, forexample, about 1 wavelength of the center frequency of operation of theradiating elements 122 (e.g., linear array 120-1 may be horizontallyspaced apart from linear array 120-2 by about a wavelength). This mayprovide horizontal spatial diversity so that the signals transmitted bythe two different linear arrays 120 that are mounted on each backplane112 may experience a different multipath fading environment. RF signalsthat are transmitted at different polarizations also tend to experiencedifferent amounts of fading, even when the signals are transmitted alongthe same physical path. Accordingly, the base station antenna 100 maytransmit signals on four paths that will be highly decorrelated,enabling throughput improvements via the implementation of MIMO.

It is anticipated that the base station antenna 100 may exhibit goodperformance. The base station antenna 100, however, may be larger andmore expensive than desirable for some applications. In particular, thebase station antenna 100 requires a total of six linear arrays 120, withthe linear arrays 120 on each backplane 112 separated by approximately awavelength or more. This increases the footprint of the base stationantenna 100. Additionally, the base station antenna 100 includes a totalof thirty-six radiating elements 122.

FIG. 5A is a schematic diagram illustrating a small cell base stationantenna 200 that uses polarization diversity and vertical spatialdiversity to implement 4× MIMO capabilities. FIGS. 5B and 5C are graphsillustrating azimuth and elevation cross-sections of the antenna beam ofthe small cell antenna 200.

As shown in FIG. 5A, the small cell base station antenna 200 includes atriangular tubular reflector assembly 210. The base station antenna 200further includes six linear arrays 220-1 through 220-6 of radiatingelements 122. Each face of the reflector assembly 210 may comprise abackplane 212-1, 212-2, 212-3. Each backplane 212 may comprise a unitarystructure or may comprise a plurality of structures that are attachedtogether. Each backplane 212 may comprise, for example, a reflector thatserves as a ground plane for the radiating elements 222 of the lineararrays 220. In some embodiments, the backplanes 212-1, 212-2, 212-3 maycomprise a unitary or monolithic structure that serves as all threebackplanes 212.

In contrast to the base station antenna 100 described above, which useshorizontal separation between the linear arrays 120, the base stationantenna 200 uses vertical separation. In particular, as shown in FIG.5A, linear arrays 220-1, 220-4 are mounted on backplane 212-1, lineararrays 220-2, 220-5 are mounted on backplane 212-2, and linear arrays220-3, 220-6 are mounted on backplane 212-3, where each linear array 220includes three radiating elements 222, and the two linear arrays 220 oneach backplane 212 are vertically stacked. Dashed boxes are included onbackplane 212-1 to more clearly illustrate the radiating elements 222that form linear arrays 220-1 and 220-4. Each radiating element 222 maybe implemented, for example, using the radiating element design shown inFIGS. 3A-3B (although each radiating element 222 may be mounted on itsown feedboard 128). The base station antenna 200 may also include thevarious other elements, described above, that are included in the basestation antenna 100, modified accordingly to account for the fact thatthe base station antenna 200 only includes half the number of radiatingelements included in base station antenna 100.

The base station antenna 200 may also implement 4× MIMO by transmittingan RF signal at two different polarizations through two different setsof three linear arrays (namely linear arrays 220-1, 220-3, 220-5 andlinear arrays 220-2, 220-4, 220-6). FIG. 5B illustrates the resultingantenna beam (azimuth plane), which has an omnidirectional pattern. Thelinear arrays 220 on each backplane 212 are spaced apart vertically toprovide vertical spatial diversity so that the RF signals transmitted bythe two different linear arrays 220 that are mounted on each backplane212 may experience a different multipath fading environment.

As shown in FIG. 5B, the base station antenna 200 generates anomnidirectional antenna pattern in the azimuth plane. However, becausethe linear arrays 220 only include half the number of radiating elements222 as the linear arrays 120 of radiating elements 122 (and hence areonly half as long in the vertical direction), the gain of base stationantenna will be about 3 dB less than the gain of base station antenna100. Thus, it is anticipated that the base station antenna 200 willunder perform as compared to the base station 100. Additionally, asshown in FIG. 5C, base station antenna 200 has a significantly largerbeamwidth in the elevation plane, which results in increased levels ofinterference with adjacent base stations and/or an overlying macro cell.Furthermore, in most situations, vertical separation between lineararrays does not lead to as much signal decorrelation as does horizontalseparation (as in base station antenna 100) because moststructures/obstacles that scatter RF signals are located to the sides ofthe user terminals that communicate with the base station as opposed tobeing located above/below the user terminal. This effect may be reduced,but not eliminated, by making the vertical separation between adjacentlinear arrays 220 in base station antenna 200 greater than thehorizontal separation between the linear arrays 120 in base stationantenna 100. Moreover, the small cell environment tends to be anenvironment where the difference in performance between horizontally andvertically separated linear arrays is the least, making verticallyseparated linear arrays at least a possibility for small cell basestation antennas. It should also be noted that the base station antenna200 is a simpler and cheaper design as it employs only half as manyradiating elements as the base station antenna 100.

FIG. 6A is a schematic diagram illustrating a small cell base stationantenna 300 according to embodiments of the present invention that formstwo peanut shaped patterns to provide small cell coverage with MIMOcapabilities. Herein, a peanut shaped pattern refers to an antennapattern having a bi-lobed cross-section through the azimuth plane, wherethe two lobes extend away from the antenna in opposite directions. FIGS.6B and 6C are graphs illustrating azimuth and elevation cross-sectionsof the antenna beam of the small cell antenna 300.

As shown in FIG. 6A, the small cell base station antenna 300 includes arectangular tubular reflector assembly 310. The base station antenna 300includes a total of four linear arrays 320-1 through 320-4 of radiatingelements 322. Each face of the reflector assembly 310 may comprise abackplane 312-1 through 312-4. Each backplane 312 may comprise a unitarystructure or may comprise a plurality of structures that are attachedtogether. Each backplane 312 may comprise, for example, a reflector thatserves as a ground plane for the radiating elements 322 of the lineararrays 320 mounted thereon.

Each linear array 320 is mounted on a respective one of the backplanes312, and may be oriented vertically with respect to the horizon when thebase station antenna 300 is mounted for use. In the depicted embodiment,each linear array 320 includes a total of six radiating elements 322. Itwill be appreciated, however, that other numbers of radiating elements322 may be included in the linear arrays 320. Each radiating element 322may be implemented, for example, using the radiating element designshown in FIGS. 3A-3B. The base station antenna 300 further includes aradome 360 that covers and protects the radiating elements 322 and othercomponents of the base station antenna 300.

The base station antenna 300 may further include a number ofconventional components that are not depicted in FIG. 6A. For example, aplurality of circuit elements and other structures may be mounted withinthe reflector assembly 310. These circuit elements and other structuresmay include, for example, phase shifters for one or more of the lineararrays 320, remote electronic tilt (RET) actuators for mechanicallyadjusting the phase shifters, one or more controllers, cablingconnections, RF transmission lines and the like. Mounting brackets (notshown) may also be provided for mounting the base station antenna 300 toanother structure such as an antenna tower or utility pole.

FIG. 7 illustrates an embodiment of feed networks 350-1 through 350-4that may be used to pass RF signals between a base station radio 42 andthe radiating elements 322 of base station antenna 300. As shown in FIG.7, the radio 42 is again a four port device having ports 44-1 through44-4. Duplexing of the transmit and receive channels is performedinternal to the radio 42, so each port 44 on the radio 42 passes bothtransmitted and received RF signals. The provision of four ports 44 onradio 42 allows the radio 42 to feed signals to two different subsets ofthe linear arrays 320 of base station antenna 300 at two different(orthogonal) polarizations. Since the base station antenna 300 has slant−45°/+45° cross-dipole radiating elements 322, the two polarizationswill be referred to as the −45° and the +45° polarizations. Fourconnectors 352 may be provided on base station antenna 300 and cables 46(e.g., coaxial cables) may connect each port 44 on the radio 42 to arespective one of these RF connectors 352.

As shown in FIG. 7 the first port 44-1 of radio 42 is coupled to theradiators 126 of the radiating elements 322 of linear arrays 320-1,320-3 that are arranged to transmit/receive signals having a −45°polarization via a first 1×2 power splitter/combiner 370-1. An RFtransmission line (e.g., a coaxial cable) may extend between theconnector 352 and the splitter/combiner 370-1. The 1×2 splitter/combiner370-1 may split RF signals received from port 44-1 into two equal powersub-components. Each output of the splitter 370-1 may be fed to arespective phase shifter 380-1, 380-3 that is associated with arespective linear array 320-1, 320-3. Similarly, the second port 44-2 ofradio 42 is coupled to the radiators 126 of the radiating elements 322of linear arrays 320-1, 320-3 that are arranged to transmit/receivesignals having a +45° polarization via a second 1×2 powersplitter/combiner 370-2. The splitter/combiner 370-2 may split RFsignals received from port 44-2 into equal power sub-components that arefed to respective phase shifters 382-1, 382-3 that are associated withthe respective linear arrays 320-1, 320-3. The third port 44-3 of radio42 is coupled to the radiators 126 of the radiating elements 322 oflinear arrays 320-2, 320-4 that are arranged to transmit/receive signalshaving a −45° polarization via a third power splitter/combiner 370-3which splits RF signals received from port 44-3 into equal powersub-components that are fed to respective phase shifters 380-2, 380-4that are associated with linear arrays 320-2, 320-4, respectively. Thefourth port 44-4 of radio 42 is coupled to the radiators 126 of theradiating elements 322 of linear arrays 320-2, 320-4 that are arrangedto transmit/receive signals having a +45° polarization via a fourthsplitter/combiner 370-4 which splits RF signals received from port 44-4into equal power sub-components that are fed to respective phaseshifters 382-2, 382-4 that are associated with linear arrays 320-2,320-4, respectively.

As shown in FIG. 7, each phase shifter 380, 382 may split the RF signalsinput thereto three ways (and the power split may be equal or unequal)and may apply a phase taper across the three sub-components of the RFsignal to, for example, apply an electronic downtilt to the antenna beamthat is formed when the sub-components of the RF signal are transmitted(or received) through the respective linear arrays 320. Each of theoutputs of each phase shifter 380, 382 may be connected to a respectiveone of three feedboards 128 that are included in each linear array 320.The radio 42 may thus transmit an RF signal through four different pathsthrough base station antenna 300, namely a first path using the −45°radiators 126 of the radiating elements 322 of linear arrays 320-1,320-3, a second path using the +45° radiators 126 of the radiatingelements 322 of linear arrays 320-1, 320-3, a third path using the −45°radiators 126 of the radiating elements 322 of linear arrays 320-2,320-4 and a fourth path using the +45° radiators 126 of the radiatingelements 322 of linear arrays 320-2, 320-4.

Unlike base station antennas 100 and 200 described above, base stationantenna 300 creates two distinct antenna patterns, since the antennabeam generated by linear arrays 320-1 and 320-3 is oriented differentlythan the antenna beam generated by linear arrays 320-2 and 320-4. Thetwo distinct antenna patterns can best be seen with reference to FIG.6B, which illustrates the simulated antenna pattern (azimuth plane) forthe base station antenna 300. As shown in FIG. 6B, the first and thirdlinear arrays 320-1, 320-3 may together form a first antenna beam 392-1that has a peanut-shaped cross-section in the azimuth plane. Likewise,the second and fourth linear arrays 320-1, 320-3 may together form asecond antenna beam 392-2 that has a peanut-shaped cross-section in theazimuth plane. Together, the antenna beams 392-1, 392-2 may provide anomnidirectional antenna pattern in the azimuth plane. FIG. 6Cillustrates the simulated antenna pattern in the elevation azimuth planefor the base station antenna 300. As can be seen, the elevation patternmay be similar to the elevation pattern for the base station antenna 100depicted at FIG. 2D above.

It will appreciated that many modifications may be made to the antennasdescribed above without departing from the scope of the presentinvention. As one example, simpler feed networks may be used in otherembodiments. For example, the feed networks 350 illustrated in FIG. 7include phase shifters 380, 382 which allow electronic adjustment of theelevation angle of the resulting antenna beams 392. In otherembodiments, the remote electronic downtilt capabilities may be omittedentirely. In such embodiments, the phase shifters 380, 382 may bereplaced with simple power splitter/combiners that do not perform anyphase shifting. Thus, it will be appreciated that a wide variety ofdifferent feed networks may be used depending upon the specificcapabilities implemented in the antennas according to embodiments of thepresent invention.

Thus, pursuant to some embodiments of the present invention, basestation antenna are provided that include first through fourth lineararrays of radiating elements that are mounted above respective firstthrough fourth backplanes. These antennas include a first feed networkthat is coupled to the first and third linear arrays of radiatingelements and a second feed network that is coupled to the second andfourth linear arrays of radiating elements. The first linear array ofradiating elements is positioned generally opposite the third lineararray of radiating elements, and the second linear array of radiatingelements is positioned generally opposite the fourth linear array ofradiating elements. The first and third linear arrays of radiatingelements may be configured to generate a first antenna beam that has apeanut-shaped cross-section in the azimuth plane, and the second andfourth linear arrays of radiating elements may be configured to generatea second antenna beam that has a peanut-shaped cross-section in theazimuth plane.

Pursuant to further embodiments of the present invention, base stationantennas are provided that include a first set of radiating elementsthat are configured to generate a first antenna beam that covers a firstsector in an azimuth plane and a third sector in the azimuth plane and asecond set of radiating elements that are configured to generate asecond antenna beam that covers a second sector in the azimuth plane anda fourth sector in the azimuth plane, where the second sector is betweenthe first sector and the third sector and the fourth sector is betweenthe first sector and the third sector and opposite the second sector.This can be seen, for example, with reference to FIG. 6B, where thecross-section in the azimuth plane is shown divided into four quadrantsor sectors 394-1 through 394-4. The first antenna beam 392-1 covers thefirst and third sectors 394-1 and 394-3, while the second antenna beam392-2 covers the second and fourth sectors 394-2 and 394-4. As can beseen the second sector 394-2 is between the first and third sectors394-1 and 394-3, as is the fourth sector 394-4. The azimuth beamwidthsof each sector 394 may be approximately the same.

FIGS. 8 and 9 are graphs comparing the simulated performance of the basestation antenna 300 as compared to the base station antennas 100 and200, respectively.

In particular, FIG. 8 illustrates the simulated capacity of a small cellbase station using the base station antenna 300 to the simulatedcapacity of a small cell base station using the base station antenna 100for CDF values ranging from 0 to 1. As shown in FIG. 8, whileperformance is similar, the base station antenna 300 supports highercapacity for CDF values of 0.5-0.7. As noted above, the base stationantenna 300 only includes two thirds the number of radiating elements(24 versus 36) that are included in base station antenna 100, and hencebase station antenna 300 may be smaller and significantly cheaper thanbase station antenna 100, while supporting the same or even greaterthroughput.

The improved performance for base station antenna 300 as compared tobase station antenna 100 that is shown in FIG. 8 may occur because theazimuth antenna pattern for base station antenna 300 are moredirectional and hence have higher gain than the azimuth antenna patternfor base station antenna 100. On the transmit side the higher linkbudget provided by the increased antenna gain outweighs the benefit ofgoing advantage seen with antenna 300 outweighs the benefit that 4× MIMOtransmission techniques have over 2× MIMO. This may occur because 4×MIMO works best when the signal-to-noise ratio is really high and thesehigh signal-to-noise ratio levels may be difficult to achieve in a realworld environment unless the user terminal is very close to the basestation. On the receive side, the discrimination given by thedirectional azimuth patterns (which limits interference from other userterminals) outweighs the diversity gain from having four receive pathsinstead of two receive paths.

Some operators may deploy radios that have two transmit paths and fourreceive paths which may be used for 2× MIMO transmission techniques andfour-way receiver diversity. The antennas according to embodiments ofthe present invention may be used with such radios. When the radios havetwo transmit paths and four receive paths, the two transmit ports may beone polarization from linear arrays that form the first peanut-shapedantenna pattern 392-1 and the opposite polarization from the lineararrays that form the second peanut-shaped pattern 392-2. This willprovide good coverage while still providing 2× MIMO where the beamsoverlap (and gain is lowest). In such embodiments, the high gain may berelied upon to make up for the reduced amount of transmission pathdiversity.

FIG. 9 illustrates the simulated capacity of a small cell base stationusing the base station antenna 300 to the simulated capacity of a smallcell base station using the base station antenna 200 for CDF valuesranging from 0 to 1. As shown in FIG. 9, the base station antenna 300supports higher capacity for almost the entire range of CDF values. Thebase station antenna 300 does include more radiating elements than basestation antenna 200 (24 versus 18), but as shown in FIG. 9, this resultsin a substantial increase in capacity.

The modelling results of FIGS. 8 and 9 suggest that longer linear arrayswith azimuth (horizontal) spatial diversity may provide improvedperformance as compared to stacked linear arrays that have elevation(vertical) spatial diversity and lower gain. The results also suggestthat antennas that form antenna beams having orthogonal peanut-shapedcross-sections in the azimuth plane (e.g., the antenna of FIG. 6A) mayprovide improved performance as compared to the tri-sector designsillustrated in FIGS. 2A and 5A.

While FIG. 6A illustrates a single-band base station antenna thatgenerates antenna beams having orthogonal peanut-shaped cross-sectionsin the azimuth plane, it will be appreciated that multi-band antennasmay also be provided. For example, FIG. 10 is a schematic view of oneface of a multi-band small cell base station antenna 400 according tofurther embodiments of the present invention. The base station antenna400 may be identical to the base station 300 described above, exceptthat the base station antenna 400 includes a second linear array ofradiating elements on each of the four backplanes 412 to providemulti-band capabilities.

As shown in FIG. 10, the antenna 400 includes a rectangular tubularreflector assembly 410. The base station antenna 400 includes fourhigh-band (e.g., 2.0 GHz) linear arrays 430 of radiating elements 432,only two of which is visible in the schematic view of FIG. 10. Each faceof the reflector assembly 410 may comprise a backplane 412. Eachhigh-band linear array 430 is mounted on a respective one of thebackplanes 412. In the depicted embodiment, each high-band linear array430 includes a total of five radiating elements 432.

The base station antenna 400 further includes four low-band (e.g., 800MHz) linear arrays 420 of radiating elements 422, only two of which isvisible in the schematic view of FIG. 10. A low-band linear array 420may be mounted on a respective one of the backplanes 412 adjacent thehigh-band linear array 430. In the depicted embodiment, each low-bandlinear array 420 includes a total of two radiating elements 422.

In the above-described embodiment, all four backplanes 412 of basestation antenna 400 have the same design. As shown in FIG. 11, pursuantto a further embodiment of the present invention, a modified version ofbase station antenna 400 (referred to herein as base station antenna401) is provided that only implements 2× MIMO in the low-band. In thisembodiment, the low-band radiators 422 are only included on backplanes412-1 and 412-3 and are omitted from backplanes 412-2 and 412-4. Thedepths of the respective nulls that are generated in the azimuth patternat the corners where the edges of the backplanes 412 meet are a functionof frequency. Thus, while relatively deep nulls may be generated in thehigher band (resulting in the peanut-shaped pattern in the azimuth planeshown in FIG. 6B), the nulls generated in the lower band (which may be,for example, at a frequency that is 2.5 times less than the frequency ofthe high-band) may be much shallower. Thus, in some embodiments, asomewhat omnidirectional pattern may be generated in the azimuth planeusing only one pair of linear arrays 420 that are mounted on oppositesides of the tubular rectangular reflector assembly 410. Accordingly, insome embodiments, the base station antenna 401 may implement 4× MIMO inthe high-band and may only implement 2× MIMO in the low-band by omittingthe low-band linear arrays 420 on backplanes 412-2 and 412-4.

FIG. 12 illustrates one backplane 512 of a small cell base stationantenna 500 according to further embodiments of the present invention.The base station antenna 500 is similar to the base station antenna 401described above with reference to FIG. 11, but it further includes twoadditional sets of linear arrays of radiating elements that operate intwo additional frequency bands to provide a four-band small cell basestation antenna. The four frequency bands may be, for example, the 800MHz frequency band, the 2.0 GHz frequency band, the 3.5 GHz frequencyband and the 5.0 GHz frequency band. Only one of the four backplanes 512of base station antenna 500 is illustrated to simplify the drawing.

As shown in FIG. 12, backplane 512 may include a total of four lineararrays 520, 530, 540, 550 mounted thereon. Linear array 520 includes tworadiating elements 522 and may operate in the lowest frequency band ofoperation (e.g., the 800 MHz frequency band). Linear array 520 may beidentical to linear array 420 discussed above. As noted above, in someembodiments, only two linear arrays 520 may be included on antenna 500so that 2× MIMO is implemented in the lowest frequency band as opposedto 4× MIMO.

Linear array 530 includes a total of five radiating elements 532 and maybe identical to linear array 430 discussed above. Linear array 530 mayoperate in the second lowest frequency band of operation (e.g., the 2GHz frequency band). Base station antenna 500 may include a total offour linear arrays 530 in some embodiments, namely one on each of thefour backplanes 512 of the tubular rectangular reflector housing 510.

Linear array 540 includes a total of six radiating elements 542. Lineararray 540 may operate in the second highest frequency band of operation(e.g., the 3.5 GHz frequency band). Base station antenna 500 may includea total of four linear arrays 540 in some embodiments, namely one oneach of the four backplanes 512 of the tubular rectangular reflectorhousing 510. The number of radiating elements 542 included in eachlinear array 540 may vary widely. In some embodiments, a singleradiating element 542 may be included in each linear “array” 540.

Linear array 550 includes a total of seven radiating elements 552.Linear array 550 may operate in the highest frequency band of operation(e.g., the 5.5 GHz frequency band). Base station antenna 500 may includea total of two linear arrays 550 in some embodiments, which may bemounted on opposed backplanes (e.g., backplanes 512-1 and 512-3 orbackplanes 512-2 and 512-4) of the tubular rectangular reflector housing510. The number of radiating elements 552 included in each linear array550 may vary widely. In some embodiments, a single radiating element 552may be included in each linear “array” 550.

Pursuant to further embodiments of the present invention, small cellbase station antennas are provided that have feed networks that feed atleast some of the linear arrays thereof out-of-phase. Such out-of-phasefeeding may provide improved performance in some circumstances,particularly with respect to signals in lower frequency ranges such asfrequency ranges below 3 GHz, although embodiments of the presentinvention are not limited to such frequency ranges.

For example, FIG. 13A illustrates a small cell base station antenna 600according to embodiments of the present invention that implementsout-of-phase feeding. The antenna 600 may be very similar to the basestation antenna 401 described above with reference to FIG. 11. As shownin FIG. 13A, the antenna 600 includes a rectangular tubular reflectorassembly 610 that has four faces and a generally rectangularcross-section. The antenna 600 further includes two low-band (e.g., 800MHz) linear arrays 620-1, 620-2 of radiating elements 622. The lineararrays 620 may be mounted facing outwardly on opposed faces of thetubular reflector assembly 610. In the depicted embodiment, eachlow-band linear array 620 includes two low-band radiating elements 622.The base station antenna 600 does not include any high-band lineararrays. The base station antenna 600 may implement 2× MIMO in thelow-band.

In contrast to the small cell base station antenna 401 of FIG. 11, thesmall cell base station antenna 600 of FIG. 13A includes feed networks(not shown, but see FIGS, 14A and 14B) that provide out-of-phase feedingto the two linear arrays 620-1, 620-2. In particular, as with theembodiments described above, an RF signal is output from a radio (notshown) and then split and fed to the two linear arrays 620-1, 620-2, andthen further split so as to be fed to the radiating elements 622thereof. However, in the embodiment of FIG. 13A, the phase of thesub-components of the RF signal that are provided to the radiatingelements 622 of linear array 620-1 is made to be different than thephase of the sub-components of the RF signal that are provided to theradiating elements 622 of linear array 620-2. It has been discoveredthat such out-of-phase feeding of the linear arrays 620-1, 620-2 mayresult in a broader bi-directional pattern that may be closer in shapeto an omnidirectional pattern in the azimuth plane than the antennapattern that results when the radiating elements 622 of the lineararrays 620-1, 620-2 are fed in-phase.

In some embodiments, the linear arrays 620-1 and 620-2 may be fed in“anti-phase” where the phase of the sub-components of the RF signal thatare fed to the respective radiating elements 622 of linear array 620-1are approximately 180 degrees out-of-phase with respect to thesub-components of the RF signal that are fed to the respective radiatingelements 622 of linear array 620-2. FIGS. 13B and 13C illustrate theimprovement that this out-of-phase feed arrangement can provide in theshape of the antenna beam in the azimuth plane. In particular, FIG. 13Bis a graph illustrating a cross-section in the azimuth plane of theantenna beam that would be generated by the small cell base stationantenna 600 if the linear arrays 620-1, 620-2 were fed in-phase (i.e.,the phase of the sub-components of the RF signal fed to the radiatingelements 622 of each linear array 620-1, 620-2 was the same). As shownin FIG. 13B, the resulting antenna beam has a cruciform shape having twomain lobes (that have peaks at the positions 12:00 and 6:00 in FIG. 13Bif the plot in FIG. 13B is viewed as the face of a clock) and two minorlobes (that have peaks at the positions 3:00 and 9:00 in FIG. 13B).While not shown in FIG. 13B, in the particular example modelled, thepeak directivity of the antenna beam was 7.2 dBi, with the peakdirectivity occurring at the 12:00 and 6:00 positions in FIG. 13B.

FIG. 13C is a graph illustrating a cross-section in the azimuth plane ofthe antenna beam that is generated by the small cell base stationantenna 600 when the linear arrays 620-1, 620-2 are fed in anti-phase(i.e., the phase of the sub-components of the RF signal that are fed tothe radiating elements 622 of linear array 620-1 are approximately 180degrees out of phase with respect to the sub-components of the RF signalthat are fed to the radiating elements 622 of linear array 620-2). Asshown in FIG. 13C, by feeding the antenna 600 in anti-phase, the minorpeaks that were present in the azimuth pattern of the antenna beam ofFIG. 13B are replaced instead with nulls. Additionally, the main beamsat the 12:00 and 6:00 positions are broadened substantially. The peakdirectivity of the antenna beam of FIG. 13C was 4.3 dBi, with the peakdirectivity occurring near the 1:00, 5:00, 7:00 and 11:00 positions inFIG. 13C.

The performance of a small cell base station antenna is typically drivenby the portions of the antenna beam that have the worst performance inthe coverage area of the antenna, as it these areas that tend to limitcapacity/coverage. As can be seen by comparing FIGS. 13B and 13C, byfeeding the linear arrays 620-1 and 620-2 in anti-phase the maximumdirectivity of the antenna beam is reduced, but the regions where theantenna directivity exceeds a pre-determined level may be increased.Accordingly, by feeding the linear arrays 620-1, 620-2 of antenna 600out-of-phase it may be possible to increase the coverage area of theresulting antenna beam.

When fed out-of-phase, the small cell base station antenna 600 stilldoes not have a conventional omnidirectional antenna pattern. However,it may generate an antenna beam that provides something close toomnidirectional coverage. For example, when fed in anti-phase, theantenna 600 may be expected to provide coverage for between perhapstwo-thirds and three quarters of the 360 degrees that constitute theazimuth plane. As small cell base station antennas are often deployed toprovide increased capacity within small regions of the coverage area ofa macrocell base station (and may, for example operate in differentfrequency bands than the macrocell base station in order to avoidinterference with the macrocell base station), gaps in the coverage ofthe small cell base station antenna may be acceptable as mobile userswithin these “gap” regions may be served by the macrocell base station.

One advantage of the small cell base station antenna 600 as compared toa similar antenna that includes an additional linear array 620 ofradiating elements on the other two faces of the tubular reflectorassembly 610 is that the number of radiating elements, feed networks,phase shifters and splitters may be cut in half when only two lineararrays 620-1, 620-2 are provided. This may significantly reduce thecomplexity, weight and the cost of the antenna, and may allow for asmall reduction in the overall size of the antenna. While improvedperformance may be obtained by adding the two extra linear arrays 620 onthe other two faces of the rectangular tubular reflector assembly 610,the associated cost may not be worth the increase incapacity/performance in many cases, particularly if the small cell basestation antenna 600 can provide something relatively close toomnidirectional coverage. This is particularly true in cases where thesmall cell base station antenna is located within a the coverage regionof a macrocell base station.

While FIG. 13C illustrates a scenario where the linear arrays 620-1,620-2 of antenna 600 are fed with RF signals that are approximately 180degrees out of phase, it will be appreciated that embodiments of thepresent invention are not limited thereto. For example, FIG. 13D is agraph illustrating a cross-section in the azimuth plane of the antennabeam that is generated by the small cell base station antenna 600 whenthe linear arrays 620-1, 620-2 are fed with RF signals that are 170degrees out-of-phase with respect to each other. As shown in FIG. 13D,the resulting antenna pattern is quite similar to the antenna patternshown in FIG. 13C. The peak directivity for the antenna pattern of FIG.13D is 4.5 dBi, which is actually slightly higher than the anti-phasefeeding case of FIG. 13C. Moreover, the coverage in the azimuth plane isalmost identical to that shown in FIG. 13C. Notably, the antenna beam ofFIG. 13D is not perfectly symmetrical, although the small degree ofanti-symmetry is unlikely to have a significant effect on performance.

It will also be appreciated that in some cases out-of-phase feeding mayresult in antenna beams that are farther away from an omnidirectionalantenna beam than would be achieved with in-phase feeding. For example,FIG. 13E is a graph illustrating a cross-section in the azimuth plane ofthe antenna beam that is generated by the small cell base stationantenna 600 when the linear arrays 620-1, 620-2 are fed with RF signalsthat are 90 degrees out-of-phase with respect to each other. As shown inFIG. 13E, the resulting antenna pattern is highly asymmetric and in manycases would only provide sufficient gain over a small range of azimuthangles.

In some embodiments of the present invention, a small cell base stationantenna may be provided that includes a first set of radiating elementsthat are arranged as a first linear array of radiating elements and asecond set of radiating elements that are arranged as a second lineararray of radiating elements. The second linear array may be mountedopposite the first linear array and pointing in a different directionthan the first linear array. The base station antenna may furtherinclude a feed network that couples the first and second sets ofradiating elements to a radio, wherein the feed network is configured tofeed the first set of radiating elements out-of-phase with respect tothe second set of radiating elements.

As shown in FIG. 13A above, in some embodiments, the first linear array620-1 may point in a first direction in the azimuth plane and the secondlinear array 620-2 may point in a second direction in the azimuth planethat is rotated in the azimuth plane by approximately 180 degrees fromthe first direction. In some embodiments, the first set of radiatingelements 622 that form the first linear array 620-1 may be fed withrespective sub-components of an RF signal are approximately 180 degreesout-of-phase with respect to the respective sub-components of an RFsignal that are second set of radiating elements 622 that form thesecond linear array 620-2. It will be appreciated, however, thatanti-phase feeding (i.e., a 180 degree difference in the phases of thesub-components of the RF signal that are fed to the respective lineararrays 620-1, 620-2) of the linear arrays 620-1, 620-2 is just oneexample embodiment. In other embodiments, the first set of radiatingelements 622 that form the first linear array 620-1 may be fedout-of-phase with respect to the second set of radiating elements 622that form the second linear array 620-2 by anywhere between 135 degreesand 225 degrees.

In some embodiments, the first and second sets of radiating elements 622may each be configured to operate in a frequency range that is within afrequency range of between 600 MHz and 1 GHz. In some embodiments, thefirst and second linear arrays 620-1, 620-2 may each include tworadiating elements 622, although embodiments of the present inventionare not limited thereto.

In some embodiments, each radiating element 622 in the first and secondsets of radiating elements 620-1, 620-2 may be a dual-polarizedradiating element 622 that includes a first radiator 626-1 that isconfigured to transmit and receive RF signals having a firstpolarization and a second radiator 626-2 that is configured to transmitand receive RF signals having a second polarization that is opposite thefirst polarization. In such embodiments, a pair of feed networks may beincluded in the antenna 600, where the first feed network couples thefirst radiators 626-1 of the radiating elements 622 of the first andsecond linear arrays 620-1, 620-2 to a first radio (not shown), and thesecond feed network couples the second radiators 626-2 of the radiatingelements 622 of the first and second linear arrays 620-1, 620-2 to asecond radio (not shown). The first and second feed networks may feedthe radiators in the respective first and second linear arrays 620-1,620-2 out-of-phase.

The first and second linear arrays 620-1, 620-2 may generate an antennabeam that has a generally peanut-shaped cross-section in an azimuthplane, except that the main lobes are expanded in size so that theantenna beam can provide coverage over a substantial portion of theazimuth plane. In some embodiments, the antenna beam may providecoverage over at least half the azimuth plane. In other embodiments, theantenna beam may provide coverage over at least two thirds of theazimuth plane. In still other embodiments, the antenna beam may providecoverage over at least three quarters of the azimuth plane.

The antenna 600 may be fed out-of-phase in various ways. For example, asshown in FIG. 14A, in a first embodiment, a feed network 650 may be usedto feed the first and second linear arrays 620-1, 620-2 of radiatingelements 622. The feed network may include a delay line 660 in the feedpath to one of the linear arrays (here linear array 620-2) that injectsa phase shift of, for example, 180 degrees with respect to the RFsignals fed to the other linear array 620-1. In other embodiments, thedelay line may be replaced with other delay or phase shifting elementssuch as, for example, a phase shifter. As another example, as shownschematically in FIG. 14B, the radiating elements 622 in the firstlinear array 620-1 may be fed by a transmission line having a firstpolarity and the radiating elements 622 in the second linear array 620-2may be fed by a transmission line having a second polarity (in otherwords, the connection of the positive and negative paths of thetransmission line are reversed for the two linear arrays 620). Oneadvantage of this approach is that the phase difference between the RFsignals fed to the first and second linear arrays 620-1, 620-2 may bemaintained over the full frequency range, whereas when a delay line suchas the feed network of FIG. 14A is used the phase shift will vary acrossthe frequency band.

It will be appreciated that the out-of-phase feed techniques describedabove with reference to FIGS. 13A-13E may be applied in other frequencybands and in other ways. For example, the same techniques may be usedwith higher band radiating elements, although typically the higher thefrequency the farther the antenna beam will be from omnidirectionalcoverage in the azimuth plane. Additionally, the out-of-phase feedtechniques may also be used to provide enhanced coverage in antennasthat have, for example, four linear arrays that are configured togenerate a pair of peanut-shaped antenna patterns when the two pairs oflinear arrays are each fed in phase.

For example, FIG. 15 is a schematic diagram illustrating small cell basestation antenna 700 according to embodiments of the present inventionthat may externally appear to be identical to the base station antenna401 of FIG. 11. However, the base station antenna 700 differs from thebase station antenna 401 in that the feed networks of the base stationantenna 700 are configured to feed the linear arrays 720-1 and 720-2out-of-phase, to feed the linear arrays 730-1 and 730-3 out-of-phase,and to feed the linear arrays 730-2 and 730-4 out-of-phase. As asidefrom the out-of-phase feed networks, the elements of antenna 700 may beidentical to the similarly numbered elements of antenna 401, furtherdescription thereof will be omitted here.

FIGS. 16A-19 are schematic diagrams illustrating small cell base stationantennas according to still further embodiments of the presentinvention. In particular, FIGS. 16A-16B, 17A-17B and 18-19 illustrateadditional small cell base station antennas that have four ports for thelow-band. In each case, the antenna supports four low-band ports with anantenna package that may be the same size as, for example, the smallcell base station antennas 401 and 700 of FIGS. 11 and 15, respectively,which each have only two low-band ports in the configurations shown.

Referring first to FIG. 16A, a small cell base station antenna 800 isschematically shown that is similar to the small cell base stationantenna 401 of FIG. 11. As shown in FIG. 16A, the small cell basestation antenna 800 includes a rectangular tubular reflector assembly810 that has four high-band (e.g., 2.0 GHz) linear arrays 830 ofradiating elements 832 and four low-band (e.g., 800 MHz) linear arrays820 of radiating elements 822 mounted thereon. Each face of thereflector assembly 810 may comprise a backplane 812. A respectivehigh-band linear array 830 is mounted on each of the four backplanes812-1 through 812-4, while low-band radiating elements 822 are onlymounted on backplanes 812-1 and 812-3. Each high-band linear array 830includes a total of five radiating elements 832, while each low-bandlinear array 820 includes a single radiating element 822.

FIG. 16B illustrates the connections between a four-port radio 842 andthe low-band radiating elements 822 of the small cell base stationantenna 800. As shown in FIG. 16B, a first port 844-1 of the radio 842is coupled to a first splitter 870-1. The first splitter 870-1 splits a(transmit path) RF signal received from port 844-1 into twosub-components that are fed to the +45° dipoles of low-band radiatingelements 822-1 and 822-3 in order to generate a first, generallypeanut-shaped antenna beam having a +45° polarization. Similarly, asecond port 844-2 of the radio 842 is coupled to a second splitter870-2. The second splitter 870-2 splits a (transmit path) RF signalreceived from port 844-2 into two sub-components that are fed to the−45° dipoles of low-band radiating elements 822-1 and 822-3 in order togenerate a second, generally peanut-shaped antenna beam having a −45°polarization. A third port 844-3 of the radio 842 is coupled to a thirdsplitter 870-3. The third splitter 870-3 splits a (transmit path) RFsignal received from port 844-3 into two sub-components that are fed tothe +45° dipoles of low-band radiating elements 822-2 and 822-4 in orderto generate a second, generally peanut-shaped antenna beam having a +45°polarization. Similarly, a fourth port 844-4 of the radio 842 is coupledto a fourth splitter 870-4. The fourth splitter 870-4 splits a (transmitpath) RF signal received from port 844-4 into two sub-components thatare fed to the −45° dipoles of low-band radiating elements 822-2 and822-4 in order to generate a second, generally peanut-shaped antennabeam having a −45° polarization. In this fashion, a total of fourtransmit antenna beams may be formed to support 4×4 MIMO transmissionsor other four-port schemes.

FIG. 17A schematically illustrates another small cell base stationantenna 801 that is similar to the small cell base station antenna 800of FIG. 16A. The primary difference between small cell base stationantenna 800 and small cell base station antenna 801 is that low-bandradiating elements 822-2 and 822-4 have been moved from backplanes 812-1and 812-3, respectively, to backplanes 812-2 and 812-4, and moved fromthe lower portions of the backplanes 812 to the upper portions thereof.The small cell base station antenna 801 will once again create twogenerally peanut-shaped antenna beams at each of the +45° and −45°polarizations, and hence will support four port operation. The pointingdirections of two of these antenna beams will differ, however, due tothe relocation of low-band radiating elements 822-2 and 822-4 frombackplanes 812-1 and 812-3, respectively, to backplanes 812-2 and 812-4.The small cell base station antenna 801 may be connected to a four portradio 842 in the manner shown in FIG. 16B.

FIG. 17B schematically illustrates another small cell base stationantenna 802 that is similar to the small cell base station antenna 801of FIG. 17A. The primary difference between small cell base stationantenna 801 and small cell base station antenna 802 is that low-bandradiating elements 822-2 and 822-4 have been moved from the upperportions of backplanes 812-2 and 812-4 to the lower portions thereof.Like small cell base station antenna 801, small cell base stationantenna 802 will create two generally peanut-shaped antenna beams ineach of the +45° and −45° polarizations, and hence will support fourport operation. The small cell base station antenna 802 may also beconnected to a four port radio 842 in the manner shown in FIG. 16B.

FIG. 18 schematically illustrates another small cell base stationantenna 803 that is similar to the small cell base station antennas 801and 802 of FIGS. 17A-17B. The primary difference between small cell basestation antenna 803 and small cell base station antennas 801 and 802 isthat the low-band radiating elements 822-2 and 822-4 that are mounted onbackplanes 812-2 and 812-4 are vertically separated from the low-bandradiating elements 822-1 and 822-3 that are mounted on backplanes 812-1and 812-3. In particular, low-band radiating elements 822-2 and 822-4are mounted on the lower portions of backplanes 812-2 and 812-4,respectively, while low-band radiating elements 822-1 and 822-3 aremounted on the upper portions of backplanes 812-2 and 812-4,respectively. It will be appreciated that in other embodiments low-bandradiating elements 822-2 and 822-4 may be mounted on the upper portionsof backplanes 812-2 and 812-4, respectively, and low-band radiatingelements 822-1 and 822-3 may be mounted on the lower portions ofbackplanes 812-2 and 812-4, respectively. Like small cell base stationantennas 801 and 802, small cell base station antenna 803 will createtwo generally peanut-shaped antenna beams in each of the +45° and −45°polarizations, and hence will support four port operation. The smallcell base station antenna 803 may also be connected to a four port radio842 in the manner shown in FIG. 16B.

FIG. 10 illustrates another small cell base station antenna 400, whichhas previously been described. The small cell base station antenna 400is similar to the above-described small cell base station antennas800-803. The small cell base station antenna 400 differs from small cellbase station antennas 800-803 in that the small cell base stationantenna 400 includes two low-band radiating elements 822 per low-bandlinear array 820 instead of one low-band radiating element 822. Byproviding two low-band radiating elements 822 per linear array 820 theantenna gain in the low-band may be enhanced and the elevation beamwidthreduced.

FIG. 19 schematically illustrates another small cell base stationantenna 804 according to embodiments of the present invention. The smallcell base station antenna 804 mounts the low-band radiating elements 822in the same locations as the small cell base station antenna 400 of FIG.10, but uses a different approach for feeding these low-band radiatingelements 822. In particular, low-band radiating elements 822-1 and 822-4form a first array and low-band radiating elements 822-5 and 822-8 forma second array. These first and second arrays 820 are commonly fed by afirst radio port having a +45° polarization and by a second radio porthaving a −45° polarization to form first and second oppositely polarizedantenna patterns. Low-band radiating elements 822-3 and 822-6 form athird array and low-band radiating elements 822-7 and 822-2 form afourth array. The third and fourth arrays are commonly fed by a thirdradio port having a +45° polarization and by a fourth radio port havinga −45° polarization to form third and fourth oppositely polarizedantenna patterns. These antenna beams will have a quasi-omnidirectionalpattern shape.

In some cases, the isolation between the low-band radiating elements 822that form different antenna beams may be an important performanceparameter. The level of isolation will depend on, among other things,the physical separation between the low-band radiating elements 822 thatare used to form different antenna beams. In the above-describedembodiments, it can be seen that either or both horizontal and verticalseparation may be used. It is believed in in some cases verticalseparation may be more effective at achieving isolation than horizontalseparation, particularly in cases where the base station antenna iselongate in the vertical direction. Thus, for example, in someapplications the small cell base station antenna 800 of FIG. 16A mayexhibit enhanced isolation as compared to the small cell base stationantennas 802 and 803 of FIGS. 17A-17B. The small cell base stationantenna 804 of FIG. 18 may exhibit even better isolation as itphysically separates the low-band radiating elements 822 that formdifferent antenna beams in both the horizontal and vertical directions.

As discussed above with reference to FIGS. 13A-14B, out-of-phase feedingmay be used where the phase of the sub-components of an RF signal thatare fed to different arrays of radiating elements are made to beout-of-phase with each other. As described above, this approach maybroaden the antenna pattern. In specific embodiments, out-of-phasefeeding may be used to make peanut-shaped antenna pattern moreomnidirectional in nature.

The above described base station antennas may generate antenna beamshaving orthogonal peanut-shaped cross-sections in the azimuth plane. Asdescribed above, these antennas may have dual-polarized radiatingelements and hence each antenna may comprise a four-port antenna that iscapable of generating a total of four antenna beams having peanut-shapedcross-sections in the azimuth plane. Pursuant to further embodiments ofthe present invention, this concept may be extended by switching from areflector having a square cross-section to a reflector having across-section with eight, twelve or sixteen sided cross-sections. Asexplained below, this approach may provide antennas that can generatefour, six or eight antenna beams at each polarization that havepeanut-shaped cross-sections in the azimuth plane to provide a total ofeight, twelve or sixteen such antenna beams. Such antennas can provideenhanced capabilities such as, for example, supporting multiplecustomers with a single antenna, supporting different sub-bands usingdifferent linear arrays, or providing a beamforming antenna.

Referring to FIG. 20A, a single band small cell antenna 900 isschematically depicted that generates a pair of orthogonal antenna beams910-1, 910-2 having peanut-shaped cross-sections in the azimuth plane.The view of FIG. 20A looks down on the antenna 900 from above and hencethe antenna beams schematically depict the antenna beam shape in theazimuth plane. While not depicted in FIG. 20A, it will be understoodthat the antenna 900 may have dual-polarized radiating elements suchthat the pair of orthogonal antenna beams 910-1, 910-2 depicted in FIG.20A will be replicated at a second polarization. These additionalantenna beams are not shown in FIG. 20A to simplify the drawing. Theantenna 900 of FIG. 20A may have the design of the antenna 300 of FIG.6A that is discussed above, and hence further discussion of antenna 900will be omitted here.

FIG. 20B schematically illustrates a small cell base station antenna 920that generates two pairs of orthogonal antenna beams 930-1, 930-2;930-3, 930-4 having peanut-shaped cross-sections in the azimuth plane.The view of FIG. 20B again looks down on the antenna 920 from above andhence the antenna beams schematically depict the antenna beam shape inthe azimuth plane. Each antenna beam 930 is shown schematically in FIG.20B (and also in FIG. 20A) using a pair of ellipses, but it will beappreciated that each antenna beam 930 will have an azimuthcross-sectional shape similar to that shown in FIG. 6B and an elevationcross-section similar to that shown in FIG. 6C. While not depicted inFIG. 20B, it will be understood that the antenna 920 may havedual-polarized radiating elements such that the two pairs of orthogonalantenna beams 930-1, 930-2, 930-3, 930-4 depicted in FIG. 20B will bereplicated at the second polarization.

As shown in FIG. 20B, the antenna 920 may have an eight-sided tubularreflector 922 with an octagonal transverse cross-section. Each side faceof the reflector 922 may have a linear array 924 of radiating elements926 mounted thereon. As the linear arrays 924 are vertically oriented,only the top radiating element 926 of each linear array is visible inthe view of FIG. 20B. The linear arrays 924 on opposed side faces of thereflector 922 are commonly fed so that the two linear arrays 924 on eachset of the opposed side faces generates an antenna beam 930 having apeanut-shaped cross-section in the azimuth plane. The antenna 920 maythus have four ports for each polarization or a total of eight ports.

The antenna 920 may be used in a variety of different applications. Forexample, in some instances base station antennas may be leased tomultiple wireless operators. The base station antenna 920 may be leasedto two wireless operators, with the linear arrays 924 generating antennabeams 930-1 and 930-2 leased to the first operator and the linear arrays924 generating antenna beams 930-3 and 930-4 leased to the secondoperator. In other instances, the small cell base station antenna 920could be used by a single operator with different sets of linear arrays924 supporting different frequency bands of operation. For example, thelinear arrays 924 generating antenna beams 930-1 and 930-2 may be usedto transmit and receive PCS band RF signals (e.g., 1850-1990 MHz) andthe linear arrays 924 generating antenna beams 930-3 and 930-4 may beused to transmit and receive AWS band RF signals (e.g., 1710-1755 MHzand 2110-2155 MHz). By supporting the two different frequency bandsusing different linear arrays 924 (as opposed to shared linear arrays),diplexers may be omitted from the antenna 920 and/or radio, and PIMdistortion performance may be improved. In other instances the smallcell base station antenna 920 may be used as a beamforming antenna wherethe two sets of four linear arrays 924 or all eight linear arrays 924may be commonly fed and the sub-components of the RF signals fed to eachlinear array 924 (and the radiating elements 926 thereof) may beamplitude and/or phase weighted to adaptively change the shape of theantenna beam(s) 930 generated by the antenna 920 to provide enhancedantenna gain in the direction of users and/or to provide reduced antennagain in the direction of interference sources. The antenna beam shapemay be changed as often as on a time-slot-by-time-slot basis.

Example embodiments of small cell base station antennas that generatetwo or more pairs of orthogonal antenna beams having peanut-shapedcross-sections in the azimuth plane will now be discussed with referenceto FIGS. 21A-23.

Referring to FIG. 21A, a small cell base station antenna 1000 isschematically depicted that may generate, at each of two differentpolarizations, four antenna beams having peanut-shaped cross-sections inthe azimuth plane. The base station antenna 1000 may be similar to thebase station antenna 300 discussed above with reference to FIG. 6A,except that the base station antenna 1000 includes twice as many lineararrays of radiating elements that are mounted on a tubular reflectorhaving an octagonal cross-section so that the antenna 1000 generate atotal of eight antenna beams having peanut-shaped cross-sections in theazimuth plane.

As shown in FIG. 21A, the small cell base station antenna 1000 includesa tubular reflector assembly 1010 that has an octagonal transversecross-section. The base station antenna 1000 includes eight lineararrays 1020 of radiating elements 1022 (only four of which are visiblein the view of FIG. 21A). Each of the eight faces of the reflectorassembly 1010 may comprise a backplane 1012. The reflector 1010 maycomprise a unitary structure or may comprise a plurality of structuresthat are attached together. Each backplane 1012 may comprise a reflectorthat serves as a ground plane for the radiating elements 1022.

Each linear array 1020 is mounted on a respective one of the backplanes1012, and may be oriented vertically with respect to the horizon whenthe base station antenna 1000 is mounted for use. In the depictedembodiment, each linear array 1020 includes a total of five radiatingelements 1022, although other numbers of radiating elements 1022 may beused. As discussed above, the linear arrays 1020 on opposed faces of thereflector 1010 may be commonly fed so that the antenna 1000 includesfour pairs of commonly fed linear arrays 1020 that generate fourpeanut-shaped antenna beams at each of two polarizations. Aside from theabove-discussed differences, the base station antenna 1000 may beidentical to the base station antenna 300 discussed above, and hencefurther description thereof will be omitted.

As described above with reference to FIG. 20B, the antenna 1000 maygenerate four antenna beams that have peanut-shaped cross-sections inthe azimuth plane at each of two different polarizations, therebyproviding a total of eight antenna beams that can generatequasi-omnidirectional patterns in the azimuth plane.

FIG. 21E illustrates how the linear arrays 1020 of antenna 1000 can befed in more detail. As shown in FIG. 21E, four ports A-D may be used tofeed the radiators of radiating elements 1022 that have a firstpolarization. In particular, signals received at port A are split andfed to the radiating elements 1022 of the linear arrays 1020 onbackplanes 1012-2 and 1012-4 (in FIG. 21E reference numerals 1-8correspond to backplanes 1012-1 through 1012-8). Likewise, signalsreceived at port B are split and fed to the radiating elements 1022 ofthe linear arrays 1020 on backplanes 1012-1 and 1012-3, signals receivedat port C are split and fed to the radiating elements 1022 of the lineararrays 1020 on backplanes 1012-6 and 1012-8 and signals received at portD are split and fed to the radiating elements 1022 of the linear arrays1020 on backplanes 1012-5 and 1012-7. The antenna 1000 will include fouradditional ports (not shown) that similarly feed the radiators ofradiating elements 1022 that have the second polarization. When fed inthis fashion, antenna 1000 will generate (at each polarization) a firstpair of orthogonal antenna beams having peanut-shaped cross-sections inthe azimuth plane using the linear arrays 1020 on backplanes 1012-1through 1012-4 (namely the linear arrays 1020 on backplanes 1012-1 and1012-3 generate the first antenna beam of the pair and the linear arrays1020 on backplanes 1012-2 and 1012-4 generate the second antenna beam ofthe pair) and a second pair of orthogonal antenna beams havingpeanut-shaped cross-sections in the azimuth plane using the lineararrays 1020 on backplanes 1012-5 through 1012-8 (namely the lineararrays 1020 on backplanes 1012-5 and 1012-7 generate the first antennabeam of the pair and the linear arrays 1020 on backplanes 1012-6 and1012-8 generate the second antenna beam of the pair).

The base station antenna 1000 would typically be operated as asingle-band antenna that provides service in a single frequency band.For example, the radiating elements used in the antenna 1000 may bedesigned to transmit and receive RF signals in the 1.6-2.7 GHz operatingfrequency band (or portions thereof). While in some applications some ofthe linear arrays 1020 may be used to transmit and receive signals in afirst sub-band of the operating frequency band and other of the lineararrays 1020 may be used to transmit and receive signals in a secondsub-band of the operating frequency band, the linear arrays 1020 mayeach typically have the same radiating elements 1022. It will beappreciated, however, that in other embodiments, adjacent linear arrays1020 may have different types of radiating elements 1022 (e.g., half thearrays have radiating elements that are optimized for operation in thePCS band, while the other half of the linear arrays 1020 have radiatingelements that are optimized for operation in the AWS band).

Pursuant to further embodiments, of the present invention, the basestation antenna 1000 may be modified to support service in multiplefrequency bands. FIGS. 21B-21D illustrate several examples of multi-bandantennas having the general design of antenna 1000 of FIG. 21A.

Referring first to FIG. 21B, a multi-band base station antenna 1100 isdepicted. The base station antenna 1100 may be identical to the basestation 1000 described above, except that the base station antenna 1100includes a second linear array of radiating elements on four of theeight backplanes 1012 to provide multi-band capabilities.

In particular, the antenna 1100 includes the octagonal tubular reflectorassembly 1010 where each face thereof comprises a backplane 1012. Thebase station antenna 1100 includes eight high-band (e.g., 1-6-2.7 GHz)linear arrays 1020 of radiating elements 1022, only four of which arevisible in FIG. 21B, along with four low-band (e.g., 696-960 MHz) lineararrays 1120 of radiating elements 1122, only two of which are visible inFIG. 21B. Respective high-band linear arrays 1020 are mounted on each ofthe backplanes 1012, while respective low-band linear arrays 1120 areonly provided on every other backplane 1012. In the depicted embodiment,each low-band linear array 1120 includes a total of two radiatingelements 1122, and the low-band radiating elements 1122 of each low-bandlinear array 1120 are collinear with the high-band radiating elements1022 of the high-band linear array 1020 that is on the same backplane1012. In the depicted embodiment, all of the high-band radiatingelements 1022 on a given backplane 1012 are positioned between the twolow-band radiating elements 1122 that are mounted on the same backplane1012. In other embodiments, this need not be the case, and one or bothof the low-band radiating elements 1122 may be in more central locationson the backplane 1012. For example, the low-band radiating elements 1122may be positioned both above and below one or both of the high-bandradiating elements 1022.

The antenna 1100 is similar to the antenna 401 of FIG. 11, but theantenna 1100 is modified to include twice as many linear arrays 1020,1120 of radiating elements 1022, 1122 mounted on a tubular reflector1010 having an octagonal transverse cross-section. Additionally, in theantenna 1100 the low-band and high-band linear arrays 1020, 1120 on eachbackplane 1012 are arranged collinearly, while in antenna 401 thelow-band and high-band linear arrays 420, 430 are laterally offset fromeach other on each backplane 412. It will be appreciated that theantenna 1100, of FIG. 21B could be so that the linear arrays 1020, 1120are mounted in a laterally offset fashion on each backplane thatincludes multiple linear arrays in the manner of antenna 401 and/or thatthe antenna 401 of FIG. 11 could be modified to have collinear lineararrays in the manner of antenna 1100 according to further embodiments ofthe present invention.

As discussed above with reference to base station antenna 401, at lowerfrequencies the nulls in the center of the peanut-shaped antenna beamsare less pronounced, and hence a single peanut-shaped antenna beam mayprovide a somewhat quasi-omnidirectional antenna beam. Thus, the basestation antenna 1100 may implement 4× MIMO in the high-band for twocustomers or for two different sub-bands, and may implement 2× MIMO inthe low-band for two customers or for two different sub-bands sincelow-band linear arrays 1120 are not provided on half of the backplanes1012. It will also be appreciated that in other embodiments low-bandlinear arrays 1120 could be provided on all eight backplanes 1012 sothat the base station antenna 1100 may implement 4× MIMO in the low-bandfor two customers or for two different sub-bands.

FIG. 21C illustrates a small cell base station antenna 1200 according tofurther embodiments of the present invention. The base station antenna1200 is similar to the base station antenna 1100 described above, but inplace of the low-band linear array 1120 the base station antenna 1200includes linear arrays 1220 of radiating elements 1222 that are designedto transmit and receive signals in, the 3.5 GHz frequency band and/orthe 5.0 GHz frequency band. In the depicted embodiment, each lineararray 1220 includes two radiating elements 1222. As with antenna 1100the two linear arrays 1020, 1220 that are provided on each backplane1012 are arranged to be collinear with each other. Each linear array1220 is mounted above its corresponding linear array 1020 on therespective backplanes 1012, although the positions of the linear arrays1020, 1220 may be reversed in other embodiments, or the radiatingelements 1022, 1222 may be interleaved. The linear arrays 1020, 1220 oneach backplane 1012 may be laterally offset from each other in stillfurther embodiments.

The antenna 1200 may generate four antenna beams that have peanut-shapedcross-sections in the azimuth plane at each of two differentpolarizations, thereby providing a total of eight antenna beams that cangenerate quasi-omnidirectional patterns in the azimuth plane. Theantenna 1200 may therefore, for example, implement 4× MIMO in thehigh-band for two different operators or in two different sub-bands suchas the PCS and AWS sub-bands of the 1.6-2.7 GHz operating frequencyband. In some embodiments, the antenna 1200 may be configured to providethe same capabilities in the 3.5 GHz and/or 5.0 GHz band. This may beaccomplished by commonly feeding the 3.5/5.0 GHz linear arrays 1220 thatare on opposite backplanes 1012 to form four antenna beams at each oftwo polarizations that have peanut-shaped cross-sections in the azimuthplane. However, more commonly the antenna 1200 may be configured sothat, at each polarization, the linear arrays 1220 are divided into twogroups of four non-adjacent linear arrays 1220 that are commonly fed.Each group of four linear arrays 1220 will produce aquasi-omnidirectional antenna beam, and when configured in this fashionthe antenna 1200 may generate a total of four antenna beams forservicing the 3.5/5.0 GHz frequency bands (namely two antenna beams ateach polarization). This allows the antenna 1200 to implement 2× MIMO inthe 3.5 GHz and/or 5.0 GHz frequency bands for two customers or for twodifferent sub-bands.

FIG. 21D illustrates a small cell base station antenna 1300 according tofurther embodiments of the present invention. The base station antenna1300 is substantially a combination of the base station antennas 1100and 1200 of FIGS. 21B and 21C. As shown in FIG. 21D, the base stationantenna 1300 includes a tubular reflector assembly 1010 that has anoctagonal transverse cross-section. The base station antenna 1300includes eight linear arrays 1020 of high-band radiating elements 1022,eight linear arrays 1220 of 3.5 GHz and/or 5.0 GHz radiating elements1222, and four linear arrays 1120 of low-band radiating elements 1122.Only half of the linear arrays 1020, 1120, 1220 are visible in the viewof FIG. 21D. Each low-band linear array 1120 includes only a singleradiating element 1122 in order to make room for the linear arrays 1020and 1220 without further increasing the height of the antenna 1300.Since the elements and operation of base station antenna 1300 have beendescribed in detail above with reference to the base station antennas ofFIGS. 21A-21C, further description of the antenna 1300 will be omittedhere.

FIGS. 21A-21D illustrate several example embodiments of small cell basestation antennas that can generate an increased number of antenna beamshaving omnidirectional or quasi-omnidirectional coverage in the azimuthplane. It will be appreciated that numerous other examples are possible.For instance, while the above description of FIG. 21A states that theantenna 1000 has high-band linear arrays 1020, it will be appreciatedthat in other embodiments the radiating elements 1022 could be replacedwith radiating elements that are configured to operate in otherfrequency bands, such as the low-band, the 3.0 GHz band, the 5.0 GHzband, or some other frequency band. It will likewise be appreciated thatantennas serving other combinations of frequency bands may be provided,such as, for example, an antenna with low-band linear arrays and 3.0 GHzlinear arrays on each backplane (mounted side-by-side, collinearly or insome other fashion). Thus, it will be appreciated that FIGS. 21A-21D areprovided to generally illustrate the concept of extending the antennasaccording to embodiments of the present invention to have more than fourlinear arrays per frequency band, but are not intended to depict allsuch embodiments.

The concept of increasing the number of backplanes and linear arrays toprovide a small cell base station antenna that can generate an increasednumber of antenna beams having peanut-shaped cross-sections in theazimuth plane may be extended beyond the eight antenna beams per bandprovided with the antennas of FIGS. 21A-21D.

In particular, the concepts described above with reference to FIGS.21A-21D may be extended to provide small cell base station antennas thathave, for at least some frequency bands, twelve linear arrays that aremounted on 12-sided tubular reflectors. FIGS. 22A-22D schematicallyillustrate four example embodiments of these small cell base stationantennas. FIGS. 22A-22D are schematic plan views of the antennas thatonly illustrate a single radiating element per backplane, similar toFIGS. 20A-20B. FIGS. 22A-22B are implementations of the antennas ofFIGS. 21A-21D, respectively, extended to a 12-sided tubular reflector.

As shown in FIG. 22A, a small cell base station antenna 1400 generatessix antenna beams 1410-1 through 1410-6 that each have peanut-shapedcross-sections in the azimuth plane. The base station antenna 1400 maybe similar to the base station antenna 1000 discussed above withreference to FIG. 21A, except that the base station antenna 1000includes twelve linear arrays 1020 of high-band radiating elements 1022that are mounted on a tubular reflector 1402 having an dodecagon(12-sided) transverse cross-section. The linear arrays 1020 on opposedfaces of the tubular reflector 1402 may be commonly fed so that theantenna 1400 includes six pairs of commonly fed linear arrays 1020 thatgenerate six antenna beams 1410 having peanut-shaped cross-sections inthe azimuth plane at each of two polarizations. The antenna beams 1410are only depicted for the first of the two polarizations, as the antennabeams for the second polarization may be substantially identical to theantenna beams 1410 that are depicted in FIG. 22A. In the depictedembodiment, the radiating elements 1022 are high-band radiating elements(i.e., radiating elements that are designed to transmit and receive RFsignals in the 1.6-2.7 GHz range of portions thereof), but it will beappreciated that radiating elements designed for operation in otherfrequency and may be used in other embodiments. Aside from theabove-discussed differences, the base station antenna 1400 may beidentical to the base station antenna 1000 discussed above, and hencefurther description thereof will be omitted. The various modificationsthat can be made to the antenna 1000 that are discussed above (e.g.,using two different radiating element designs so that adjacent lineararrays 1020 have different radiating element designs) may also be madeto the antenna 1400 to provide yet additional embodiments.

As shown in FIG. 22B, a small cell base station antenna 1500 generatessix orthogonal antenna beams 1410-1 through 1410-6 as well as threeantenna beams 1510-1 through 1510-3, where all of the antenna beams1410, 1510 have peanut-shaped cross-sections in the azimuth plane. Thebase station antenna 1500 may be similar to the base station antenna1100 discussed above with reference to FIG. 21B, except that the basestation antenna 1500 includes twelve linear arrays 1020 of radiatingelements 1022 and six linear arrays 1120 of radiating elements 1122 thatare mounted on a tubular reflector 1402 having an dodecagon transversecross-section, whereas the antenna 1100 only has eight linear arrays1020 of radiating elements 1022 and four linear arrays 1120 of radiatingelements 1122 mounted on a reflector 1010 having an octagonal transversecross-section.

As shown in FIG. 22C, a small cell base station antenna 1600 generatessix orthogonal antenna beams 1410-1 through 1410-6 that havepeanut-shaped cross-sections in the azimuth plane as well as threeantenna beams 1610-1, 1610-2, 1610-3 that have generally circularcross-sections in the azimuth plane with some dips (not shown). The basestation antenna 1600 may be similar to the base station antenna 1200discussed above with reference to FIG. 21C, except that the base stationantenna 1600 includes twelve linear arrays 1020 of radiating elements1022 and twelve linear arrays 1220 of radiating elements 1222 that aremounted on a tubular reflector 1402 having an dodecagon transversecross-section, whereas the antenna 1200 only has eight linear arrays1020 of radiating elements 1022 and eight linear arrays 1220 ofradiating elements 1222 mounted on a tubular reflector 1010 having anoctagonal transverse cross-section.

FIG. 22D schematically illustrates a small cell base station antenna1700 according to further embodiments of the present invention. The basestation antenna 1700 is substantially a combination of the base stationantennas 1500 and 1600 of FIGS. 22B and 22C. As shown in FIG. 22D, thebase station antenna 1700 includes a tubular reflector assembly 1402that has an dodecagon transverse cross-section. As shown in FIG. 22D,the antenna 1700 generates, at each of two polarizations, six antennabeams 1410-1 through 1410-6 and three antenna beams 1510-1 through1510-3 that have peanut-shaped cross-sections in the azimuth plane aswell as three antenna beams 1610-1 through 1610-3 that have generallycircular cross-sections in the azimuth plane. The base station antenna1700 may be similar to the base station antenna 1300 discussed abovewith reference to FIG. 21D, except that the base station antenna 1700includes twelve linear arrays 1020 of radiating elements 1022, sixlinear arrays 1120 of radiating elements 1122 and twelve linear arrays1220 of radiating elements 1222 that are mounted on a tubular reflector1402 having an dodecagon transverse cross-section, whereas the antenna1200 only has eight linear arrays 1020 of radiating elements 1022, fourlinear arrays 1120 or radiating elements 1122 and eight linear arrays1220 of radiating elements 1222 mounted on a tubular reflector 1010having an octagonal transverse cross-section.

It should be noted that in FIGS. 22-B through 22D only the linear arrays1020 are shown to simplify the drawings, even though each of theseantennas also include either or both linear arrays 1120 and lineararrays 1220.

Pursuant to still further embodiments of the present invention, basestation antennas are provided that have 16-sided tubular reflectors. Forexample, each of the antennas illustrated in FIGS. 21A-21D may bemodified to include a 16-sided tubular reflector having a haxadecagontransverse cross-section and to include twice the number of lineararrays. FIG. 23 schematically illustrates the design of an antenna 1800that corresponds to the antenna 1000 of FIG. 21A modified to employ a16-sided tubular reflector 1802 having a haxadecagon transversecross-section and to include twice the number of linear arrays.

As shown in FIG. 23, the small cell base station antenna 1800 generateseight antenna beams 1810-1 through 1810-8 that each have peanut-shapedcross-sections in the azimuth plane. While modified versions of theantennas of FIGS. 21B-21D that have twice as many linear arrays and a16-sided tubular reflector are not illustrated in the drawings, theseantennas may be readily provided by modifying the antennas of FIGS.21B-21D in the same manner that the antenna of FIG. 21A is modified toprovide the antenna 1800 of FIG. 23.

The small cell base station antennas according to embodiments of thepresent invention may be very compact. For example, in some embodiments,the antennas utilizing square tubular reflectors may fit within atwo-foot tall radome having a diameter of 8 inches, and the antennasutilizing octagonal tubular reflectors may fit within a two-foot tallradome having a diameter of 12 inches. These antennas may also providecomparable performance to conventional small cell base station antennaswhile including fewer radiating elements, and may be cheaper tomanufacture.

The small cell antennas according to embodiments of the presentinvention that are formed on tubular reflectors having more than fourfaces (e.g., tubular reflectors having 8, 12 or 16 faces) may be used ina variety of ways. For example, in some cases, the antennas havingtubular reflectors with octagonal cross-sections may be deployed andshared by two different cellular operators. The first cellular operatormay control four of the eight ports on the antenna (e.g., the portsfeeding four non-adjacent linear arrays), while the second cellularoperator may control the other four ports on the antenna (e.g., theports feeding the remaining four linear arrays). In this fashion, asingle base station antenna may be leased or otherwise shared to provideomnidirectional small cell coverage supporting 4× MIMO on at least somefrequency bands for two different cellular operators. For embodiments ofthe present invention that include 12-sided or 16-sided tubularreflectors, the number of cellular operators that can be supported by asingle antenna may increase to three or four, respectively.

In other cases, a single cellular operator may use the full capabilitiesof the small cell antennas according to embodiments of the presentinvention that have tubular reflectors having more than four faces. Forexample, the antennas having tubular reflectors with octagonalcross-sections may be deployed and the high-band linear arrays on somefaces of the reflector may support a first sub-band of the highfrequency band (e.g., the PCS sub-band) while the remaining faces of thereflector may support a second sub-band of the high frequency band(e.g., the AWS sub-band). This may eliminate the need for diplexers toseparate the frequency bands, which may reduce cost and/or increaseperformance. Additionally, the PIM performance of the antenna may besubstantially improved by providing separate linear arrays for eachsub-band. The same approach may be used with the 3.5 GHz and 5.0 GHz subbands of the 3.5/5.0 GHz band.

In still other cases, when more than four linear arrays are provided onan antenna according to embodiments of the present invention for a givenfrequency band, the additional linear arrays may provide the antennawith capability to operate as a beamforming antenna. This may increasethe gain of the antenna, allowing for lower power transmissions whichmay reduce cost and reduce interference with other neighboring cells.Additionally, the beamforming capabilities may be used to reduce thegain of the antenna in the direction of interference sources.

It will be appreciated that any of the small cell base station antennasdisclosed herein, specifically including the antennas of FIGS. 16A-23,may be fed using in-phase feeding or out-of-phase feeding. Whenout-of-phase feeding is used, anti-phase feeding may be used or anyother amount of phase difference may be used.

The present invention has been described above with reference to theaccompanying drawings. The invention is not limited to the illustratedembodiments; rather, these embodiments are intended to fully andcompletely disclose the invention to those skilled in this art. In thedrawings, like numbers refer to like elements throughout. Thicknessesand dimensions of some elements may not be to scale.

Spatially relative terms, such as “under”, “below”, “lower”, “over”,“upper”, “top”, “bottom” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “under” or “beneath”other elements or features would then be oriented “over” the otherelements or features. Thus, the exemplary term “under” can encompassboth an orientation of over and under. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

Well-known functions or constructions may not be described in detail forbrevity and/or clarity. As used herein the expression “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention.

1. A base station antenna, comprising: a first linear array of radiatingelements that are mounted to extend outwardly from a first backplane; asecond linear array of radiating elements that are mounted to extendoutwardly from a second backplane; a third linear array of radiatingelements that are mounted to extend outwardly from a third backplane; afourth linear array of radiating elements that are mounted to extendoutwardly from a fourth backplane; a fifth linear array of radiatingelements that are mounted to extend outwardly from a fifth backplane; asixth linear array of radiating elements that are mounted to extendoutwardly from a sixth backplane; a seventh linear array of radiatingelements that are mounted to extend outwardly from a seventh backplane;an eighth linear array of radiating elements that are mounted to extendoutwardly from an eighth backplane; a first feed network that is coupledto the first and third linear arrays of radiating elements; a secondfeed network that is coupled to the second and fourth linear arrays ofradiating elements; a third feed network that is coupled to the fifthand seventh linear arrays of radiating elements; and a fourth feednetwork that is coupled to the sixth and eighth linear arrays ofradiating elements, wherein the first linear array of radiating elementsis positioned generally opposite the third linear array of radiatingelements, the second linear array of radiating elements is positionedgenerally opposite the fourth linear array of radiating elements, thefifth linear array of radiating elements is positioned generallyopposite the seventh linear array of radiating elements, and the sixthlinear array of radiating elements is positioned generally opposite theeighth linear array of radiating elements.
 2. The base station antennaof claim 1, wherein the first through eighth backplanes together definea tube.
 3. The base station antenna of claim 2, wherein the tube has agenerally octagonal transverse cross-section.
 4. The base stationantenna of claim 1, wherein the first and third linear arrays ofradiating elements are configured to generate a first antenna beam thathas a peanut-shaped cross-section in the azimuth plane, and the secondand fourth linear arrays of radiating elements are configured togenerate a second antenna beam that has a peanut-shaped cross-section inthe azimuth plane.
 5. The base station antenna of claim 4, wherein thefifth and seventh linear arrays of radiating elements are configured togenerate a third antenna beam that has a peanut-shaped cross-section inthe azimuth plane, and the sixth and eighth linear arrays of radiatingelements are configured to generate a fourth antenna beam that has apeanut-shaped cross-section in the azimuth plane.
 6. The base stationantenna of claim 1, wherein the first and third linear arrays ofradiating elements are configured to generate a first antenna beam at afirst polarization and a second antenna beam at a second polarizationthat is opposite the first polarization, and the second and fourthlinear arrays of radiating elements are configured to generate a thirdantenna beam at the first polarization and a fourth antenna beam at thesecond polarization, wherein the first and third linear arrays ofradiating elements are configured to operate as a two-input-two-outputmulti-input-multi-output (“MIMO”) antenna and the second and fourthlinear arrays of radiating elements are configured to operate as atwo-input-two-output MIMO antenna.
 7. The base station antenna of claim1, wherein the first through eight linear arrays of radiating elementsare configured to transmit and receive radio frequency (“RF”) signals ina first frequency band.
 8. The base station antenna of claim 1, furthercomprising: a ninth array of radiating elements that are mounted toextend outwardly from a ninth backplane; a tenth linear array ofradiating elements that are mounted to extend outwardly from a tenthbackplane; an eleventh linear array of radiating elements that aremounted to extend outwardly from an eleventh backplane; a twelfth lineararray of radiating elements that are mounted to extend outwardly from atwelfth backplane; a fifth feed network that is coupled to the ninth andeleventh linear arrays of radiating elements; and a sixth feed networkthat is coupled to the tenth and twelfth linear arrays of radiatingelements, wherein the ninth linear array of radiating elements ispositioned generally opposite the eleventh linear array of radiatingelements, and the tenth linear array of radiating elements is positionedgenerally opposite the twelfth linear array of radiating elements. 9.The base station antenna of claim 8, wherein the first through twelfthbackplanes together define a tube having a generally dodecagonaltransverse cross-section.
 10. (canceled)
 11. A base station antennacomprising: at least first through eighth linear arrays of radiatingelements that are radially mounted on a tubular reflector assembly asfour opposed pairs of linear arrays of radiating elements.
 12. The basestation antenna of claim 11, further comprising first through fourthports, wherein the first and third linear arrays are commonly fed viathe first port, the second and fourth linear arrays are commonly fed viathe second port, the fifth and seventh linear arrays are commonly fedvia the third port, and the sixth and eighth linear arrays are commonlyfed via the fourth port.
 13. The base station antenna of claim 11,wherein the tubular reflector assembly has one of an octagonal, adodecagon or a hexadecagon cross-section in the azimuth plane.
 14. Thebase station antenna of claim 11, wherein each opposed pair of lineararrays of radiating elements is configured to generate an antenna beamthat has a peanut-shaped cross-section in the azimuth plane.
 15. Thebase station antenna of claim 11, wherein the first through eighthlinear arrays of radiating elements are configured to operate in a firstradio frequency (RF) band.
 16. The base station antenna of claim 15,wherein each of the first through eighth linear arrays of radiatingelements is mounted on a respective one of the first through eighthbackplanes of the tubular reflector assembly, and wherein at least someof the first through eighth backplanes include a respective additionallinear array of radiating elements that is configured to operate in asecond first RF band that is different from the first RF band.
 17. Thebase station antenna of claim 16, wherein each additional linear arrayof radiating elements is collinear with a respective one of the firstthrough eighth linear arrays of radiating elements. 18-27. (canceled)28. A base station antenna, comprising: a first set of radiatingelements that are configured to generate a first antenna beam that has afirst peanut-shaped cross-section in an azimuth plane; a second set ofradiating elements that are configured to generate a second antenna beamthat has a second peanut-shaped cross-section in the azimuth plane; athird set of radiating elements that are configured to generate a thirdantenna beam that has a third peanut-shaped cross-section in an azimuthplane; a fourth set of radiating elements that are configured togenerate a fourth antenna beam that has a fourth peanut-shapedcross-section in the azimuth plane, wherein a longitudinal axis of thefirst antenna beam in the azimuth plane is rotated approximately ninetydegrees from a longitudinal axis of the second antenna beam in theazimuth plane and a longitudinal axis of the third antenna beam in theazimuth plane is rotated approximately ninety degrees from alongitudinal axis of the fourth antenna beam in the azimuth plane, andthe longitudinal axis of the third antenna beam in the azimuth plane isrotated approximately forty-five degrees from a longitudinal axis of thefirst antenna beam in the azimuth plane.
 29. The base station antenna ofclaim 28, wherein the first set of radiating elements comprises: a firstsubset of radiating elements that are arranged as a first linear arrayof radiating elements; and a third subset of radiating elements that arearranged as a third linear array of radiating elements.
 30. The basestation antenna of claim 29, wherein the second set of radiatingelements comprises: a second subset of radiating elements that arearranged as a second linear array of radiating elements, and a fourthsubset of radiating elements that are arranged as a fourth linear arrayof radiating elements.
 31. The base station antenna of claim 30, whereinthe third linear array of radiating elements is mounted opposite thefirst linear array of radiating elements and the fourth linear array ofradiating elements is mounted opposite the second linear array ofradiating elements. 32-33. (canceled)